E2 domain of amyloid precursor protein; The E2 domain is the largest of the conserved domains of the amyloid precursor protein. The structure of E2 consists of two coiled-coil sub-structures connected through a continuous helix, and bears an unexpected resemblance to the spectrin family of protein structures.E 2 can reversibly dimerize in solution, and the dimerization occurs along the longest dimension of the molecule in an antiparallel orientation, which enables the N-terminal substructure of one monomer to pack against the C-terminal substructure of a second monomer. The high degree of conservation of residues at the putative dimer interface suggests that the E2 dimer observed in the crystal could be physiologically relevant. Heparin sulfate proteoglycans, the putative ligands for the precursor present in extracellular matrix, bind to E2 at a conserved and positively charged site near the dimer interface.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  371 PPTPQPTDDVDVYFETPADDKEHSRFQKAKEQLEIRHRNRMERVRKEWEEAESQARNLPKAE-------RQTLIQHFQAM 443
Cdd:pfam12925   1 TTTPPPTDAVDPYFEHPDPRNEHESFKKAKKRLEEKHRERMTKVMKEWEEAEERYQNLPKADpkaaekfKKAMTARFQET 80

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  444 VESLEEEAASEKQQLVETHLARVEAMLNDRRRLALENYLAALQADPPRPHRILQALKRYVRAENKDRQHTIRHYQHVLAV 523
Cdd:pfam12925  81 VEALEEEAAAERQQLVETHQQRVEAHLNDRRRDALECYLQALQENPPNPHRILKALKKLLRAEQKDRRHTLRHYRHLLAS 160

                         170       180       190
                  ....*....|....*....|....*....|
gi 528508507  524 DPEKAAQMKSQVMTHLRVIEERMNQSLSLL 553
Cdd:pfam12925 161 DPEKAEQMKPQVLTHLRVIDRRMNQSLTLL 190

Kunitz domain found in the amyloid-beta precursor protein (ABPP) subfamily; This subfamily includes the amyloid-beta precursor protein (ABPP, also called APP, APPI, Alzheimer disease amyloid protein, amyloid-beta A4 protein, cerebral vascular amyloid peptide (CVAP), protease nexin II (PN2)), as well as amyloid-like protein 2 (APLP2, also called amyloid protein homolog or APPH), among others. ABPP/APPI is an inhibitor of serine proteases such as anionic and cationic trypsins. For example, APPI-4M is a variant that specifically inhibits Kallikrein (KLK)-related peptidase 6 (KLK6), which is highly upregulated in several types of cancer where its increased activity promotes cancer invasion and metastasis. Amyloid-like protein 2 (APLP2) inhibits trypsin, chymotrypsin, plasmin, factor XIA, and plasma and glandular kallikrein, and may play a role in the regulation of hemostasis. Proteins in this subfamily contain a single Kunitz domain, with a structure similar to those of other Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22607    1 VCSEQAETGPCRAMMPRWYFDVTEGKCAPFIYGGCGGNRNNFESEEYCMAVC 52

E2 domain of amyloid precursor protein; The E2 domain is the largest of the conserved domains of the amyloid precursor protein. The structure of E2 consists of two coiled-coil sub-structures connected through a continuous helix, and bears an unexpected resemblance to the spectrin family of protein structures.E 2 can reversibly dimerize in solution, and the dimerization occurs along the longest dimension of the molecule in an antiparallel orientation, which enables the N-terminal substructure of one monomer to pack against the C-terminal substructure of a second monomer. The high degree of conservation of residues at the putative dimer interface suggests that the E2 dimer observed in the crystal could be physiologically relevant. Heparin sulfate proteoglycans, the putative ligands for the precursor present in extracellular matrix, bind to E2 at a conserved and positively charged site near the dimer interface.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  371 PPTPQPTDDVDVYFETPADDKEHSRFQKAKEQLEIRHRNRMERVRKEWEEAESQARNLPKAE-------RQTLIQHFQAM 443
Cdd:pfam12925   1 TTTPPPTDAVDPYFEHPDPRNEHESFKKAKKRLEEKHRERMTKVMKEWEEAEERYQNLPKADpkaaekfKKAMTARFQET 80

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  444 VESLEEEAASEKQQLVETHLARVEAMLNDRRRLALENYLAALQADPPRPHRILQALKRYVRAENKDRQHTIRHYQHVLAV 523
Cdd:pfam12925  81 VEALEEEAAAERQQLVETHQQRVEAHLNDRRRDALECYLQALQENPPNPHRILKALKKLLRAEQKDRRHTLRHYRHLLAS 160

                         170       180       190
                  ....*....|....*....|....*....|
gi 528508507  524 DPEKAAQMKSQVMTHLRVIEERMNQSLSLL 553
Cdd:pfam12925 161 DPEKAEQMKPQVLTHLRVIDRRMNQSLTLL 190

juxtamembrane and transmembrane (JMTM) domain found in amyloid-like protein 2 (APLP-2) and similar proteins; Amyloid-like protein 2 (APLP-2), also called amyloid protein homolog (APPH), or CDEI box-binding protein (CDEBP), may play a role in the regulation of hemostasis. Its soluble form may have inhibitory properties towards coagulation factors. APLP-2 may bind to the DNA 5'-GTCACATG-3'(CDEI box). It inhibits trypsin, chymotrypsin, plasmin, factor XIA, and plasma and glandular kallikrein. This model corresponds to juxtamembrane and transmembrane (JMTM) domain of APLP-2, which consists of the intact transmembrane (TM) domain with adjacent N-terminal juxtamembrane (JM) region.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507 693 SFRPLVDDFSFGSSALIGLLVIAVAIATVIVISLVLLRKRQYGTISHGIVEVDPMLTPEERHLSKMQNHGYENPTYKYLE 772
Cdd:cd21709    1 SDGPLRDDFSFSSSALIGLLVIAVAIATVIVISLVLLRKRQYGTISHGIVEVDPMLTPEERHLNKMQNHGYENPTYKYLE 80

                 .
gi 528508507 773 Q 773
Cdd:cd21709   81 Q 81

Kunitz/Bovine pancreatic trypsin inhibitor domain; Indicative of a protease inhibitor, usually a serine protease inhibitor. Structure is a disulfide rich alpha+beta fold. BPTI (bovine pancreatic trypsin inhibitor) is an extensively studied model structure. Certain family members are similar to the tick anticoagulant peptide (TAP). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways. TAP molecules are highly dipolar, and are arranged to form a twisted two- stranded antiparallel beta-sheet followed by an alpha helix.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|...
gi 528508507  314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:pfam00014   1 ICSLPPDSGPCKASIPRWYYNPTTGTCEPFTYGGCGGNANNFESLEECESTCR 53

BPTI/Kunitz family of serine protease inhibitors; Serine protease inhibitors. One member of the family is encoded by an alternatively-spliced form of Alzheimer's amyloid beta-protein.

                           10        20        30        40        50
                   ....*....|....*....|....*....|....*....|....*....|..
gi 528508507   314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:smart00131   2 VCLLPPDTGPCGGSIPRYYYDPETGTCEPFTYGGCGGNANNFESLEECERTC 53

E2 domain of amyloid precursor protein; The E2 domain is the largest of the conserved domains of the amyloid precursor protein. The structure of E2 consists of two coiled-coil sub-structures connected through a continuous helix, and bears an unexpected resemblance to the spectrin family of protein structures.E 2 can reversibly dimerize in solution, and the dimerization occurs along the longest dimension of the molecule in an antiparallel orientation, which enables the N-terminal substructure of one monomer to pack against the C-terminal substructure of a second monomer. The high degree of conservation of residues at the putative dimer interface suggests that the E2 dimer observed in the crystal could be physiologically relevant. Heparin sulfate proteoglycans, the putative ligands for the precursor present in extracellular matrix, bind to E2 at a conserved and positively charged site near the dimer interface.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  371 PPTPQPTDDVDVYFETPADDKEHSRFQKAKEQLEIRHRNRMERVRKEWEEAESQARNLPKAE-------RQTLIQHFQAM 443
Cdd:pfam12925   1 TTTPPPTDAVDPYFEHPDPRNEHESFKKAKKRLEEKHRERMTKVMKEWEEAEERYQNLPKADpkaaekfKKAMTARFQET 80

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507  444 VESLEEEAASEKQQLVETHLARVEAMLNDRRRLALENYLAALQADPPRPHRILQALKRYVRAENKDRQHTIRHYQHVLAV 523
Cdd:pfam12925  81 VEALEEEAAAERQQLVETHQQRVEAHLNDRRRDALECYLQALQENPPNPHRILKALKKLLRAEQKDRRHTLRHYRHLLAS 160

                         170       180       190
                  ....*....|....*....|....*....|
gi 528508507  524 DPEKAAQMKSQVMTHLRVIEERMNQSLSLL 553
Cdd:pfam12925 161 DPEKAEQMKPQVLTHLRVIDRRMNQSLTLL 190

juxtamembrane and transmembrane (JMTM) domain found in amyloid-like protein 2 (APLP-2) and similar proteins; Amyloid-like protein 2 (APLP-2), also called amyloid protein homolog (APPH), or CDEI box-binding protein (CDEBP), may play a role in the regulation of hemostasis. Its soluble form may have inhibitory properties towards coagulation factors. APLP-2 may bind to the DNA 5'-GTCACATG-3'(CDEI box). It inhibits trypsin, chymotrypsin, plasmin, factor XIA, and plasma and glandular kallikrein. This model corresponds to juxtamembrane and transmembrane (JMTM) domain of APLP-2, which consists of the intact transmembrane (TM) domain with adjacent N-terminal juxtamembrane (JM) region.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528508507 693 SFRPLVDDFSFGSSALIGLLVIAVAIATVIVISLVLLRKRQYGTISHGIVEVDPMLTPEERHLSKMQNHGYENPTYKYLE 772
Cdd:cd21709    1 SDGPLRDDFSFSSSALIGLLVIAVAIATVIVISLVLLRKRQYGTISHGIVEVDPMLTPEERHLNKMQNHGYENPTYKYLE 80

                 .
gi 528508507 773 Q 773
Cdd:cd21709   81 Q 81

Kunitz domain found in the amyloid-beta precursor protein (ABPP) subfamily; This subfamily includes the amyloid-beta precursor protein (ABPP, also called APP, APPI, Alzheimer disease amyloid protein, amyloid-beta A4 protein, cerebral vascular amyloid peptide (CVAP), protease nexin II (PN2)), as well as amyloid-like protein 2 (APLP2, also called amyloid protein homolog or APPH), among others. ABPP/APPI is an inhibitor of serine proteases such as anionic and cationic trypsins. For example, APPI-4M is a variant that specifically inhibits Kallikrein (KLK)-related peptidase 6 (KLK6), which is highly upregulated in several types of cancer where its increased activity promotes cancer invasion and metastasis. Amyloid-like protein 2 (APLP2) inhibits trypsin, chymotrypsin, plasmin, factor XIA, and plasma and glandular kallikrein, and may play a role in the regulation of hemostasis. Proteins in this subfamily contain a single Kunitz domain, with a structure similar to those of other Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22607    1 VCSEQAETGPCRAMMPRWYFDVTEGKCAPFIYGGCGGNRNNFESEEYCMAVC 52

Kunitz/Bovine pancreatic trypsin inhibitor domain; Indicative of a protease inhibitor, usually a serine protease inhibitor. Structure is a disulfide rich alpha+beta fold. BPTI (bovine pancreatic trypsin inhibitor) is an extensively studied model structure. Certain family members are similar to the tick anticoagulant peptide (TAP). This is a highly selective inhibitor of factor Xa in the blood coagulation pathways. TAP molecules are highly dipolar, and are arranged to form a twisted two- stranded antiparallel beta-sheet followed by an alpha helix.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|...
gi 528508507  314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:pfam00014   1 ICSLPPDSGPCKASIPRWYYNPTTGTCEPFTYGGCGGNANNFESLEECESTCR 53

Kunitz/Bovine pancreatic trypsin inhibitor (BPTI) domain; This family contains the Kunitz domain which is a common structural fold found in a family of reversible serine protease inhibitors. This domain is thought to have evolved over 500 million years and is ubiquitous in all kingdoms of life and has been incorporated into many different genes. In general, each domain is encoded by a single exon. Some genes encode proteins with a single Kunitz domain, e.g. bovine pancreatic trypsin inhibitor (BPTI), trophoblast Kunitz domain protein (TKDP), amyloid beta-protein precursor (ABPP), as well as Kunitz-type venom peptides such as dendrotoxin. Genes that encode multiple Kunitz domains include hepatocyte growth factor activator inhibitors HAI1 and HAI2 (two domains), tissue factor pathway inhibitor TFPI1 and TFPI2 (three domains) and Caenorhabditis elegans papilin (eleven domains). In addition, the Kunitz domain has been integrated into multi-domain proteins, e.g. the collagen alpha3(VI), alpha1(VII) and alpha1(XXVIII) chains, WFIKKN1 (containing WAP, Follistatin/Kazal, Immunoglobulin, two Kunitz and NTR domains) and papilin. Furthermore, each domain within a multi-Kunitz domain protein may exhibit different protease activity, such as for the three tandemly repeated domains within both tissue factor pathway inhibitors 1 and 2. The Kunitz domain is a representative of alpha/beta proteins with irregular secondary structure stabilized by three disulfide bonds and presenting three peptide loops that can be varied without introducing much destabilization to the scaffold. Protease inhibitors meet the scaffold criteria in that they are small, stable and capable of evolving the binding activity of exposed peptide loops through targeted randomization to construct combinatorial libraries. Kunitz domain-based scaffolds have been successfully utilized to construct and select a library of protease inhibitors with the potential for therapeutic application.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd00109    1 CLLPPDPGPCRAYFPRWYYNSETGQCEEFIYGGCGGNANNFETKEECEATC 51

BPTI/Kunitz family of serine protease inhibitors; Serine protease inhibitors. One member of the family is encoded by an alternatively-spliced form of Alzheimer's amyloid beta-protein.

                           10        20        30        40        50
                   ....*....|....*....|....*....|....*....|....*....|..
gi 528508507   314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:smart00131   2 VCLLPPDTGPCGGSIPRYYYDPETGTCEPFTYGGCGGNANNFESLEECERTC 53

Kunitz domain of epididymal protease inhibitor eppin and similar proteins; This subfamily includes the Kunitz inhibitor domain protein eppin (also called Cancer/testis antigen 71 or CT71, epididymal protease inhibitor, protease inhibitor WAP7, serine protease inhibitor-like with Kunitz and WAP domains 1, or WAP four-disulfide core domain protein 7) as well as WAP four-disulfide core domain proteins 6A and 6B in mice, and similar proteins. Eppin is a serine protease inhibitor that plays an essential role in male reproduction and fertility. It modulates the hydrolysis of seminal fluid protein semenogelin 1 (SEMG1) by the serine protease kallikrein-related peptidase 3 (KLK3, PSA), provides antimicrobial protection for spermatozoa in the ejaculate coagulum, and binds SEMG1, thereby inhibiting sperm motility. Thus, eppin could potentially be used as a target for male contraception. These domains are similar to Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 528508507 313 AVCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:cd22611    1 DVCSLPKESGPCMAYFPRWWYDKETNTCSKFIYGGCQGNNNNFQSEAICQNICK 54

Kunitz domain 1 of hepatocyte growth factor activator inhibitor-1 (HAI-1); This model includes Kunitz domain 1 (KD1) of hepatocyte growth factor activator inhibitor type 1 (HAI1 or HAI-1, also known as Kunitz-type protease inhibitor 1), a membrane-bound multidomain protein essential to the integrity of the basement membrane during placental development. HAI-1 contains an extracellular region and several internal domains that include two Kunitz domains separated in sequence but spatially closed to each other, and their interdomain interactions have evolved to stimulate the inhibitory activity of an integrated Kunitz. KD1, the major inhibitory domain of HAI-1, is involved in auto-inhibition of the extracellular region via steric blockage of its active site in the HAI-1 compact tertiary structure; presence of the target protease causes changes in the HAI-1 structure to an extended conformation. HAI-1 has been shown to inhibit several serine proteases such as matripase, hepsin, trypsin, hepatocyte growth factor activator (HGFA), and prostasin. It is also important in maintaining postnatal homeostasis in many tissues, including keratinization of the epidermis, hair development, colonic epithelium integrity, proliferation and cell fate of neural progenitor cells, and tissue injury and repair. The interaction between HAI-1 and matriptase is critical for tissue morphogenesis and cellular biology. HAI-1:matriptase ratio imbalance results in tumorigenesis; slight overexpression of matriptase relative to HAI-1 causes spontaneous squamous cell carcinoma, a phenotype that can be effectively reversed back to wild type by additional expression of HAI-1, indicating the need for a tight functional relationship between the two to maintain homeostasis. The structures of these domains are similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:cd22623    6 CLAPKKVGPCRGSFPRWHYNAASGKCEEFVFGGCKGNKNNYLSEEECLSACR 57

Kunitz protease inhibitor (KPI) domain 1 (KPI-1 or K1) of tissue factor pathway inhibitor (TFPI); This model represents the first Kunitz-type domain (K1 or KPI-1) of tissue factor pathway inhibitor (TFPI or TFPI1), also known as extrinsic pathway inhibitor (EPI) or lipoprotein-associated coagulation inhibitor (LACI). TFPI down-regulates the extrinsic coagulation pathway via inhibition of activated factor X (FXa or Xa) and FVIIa (VIIa). It inhibits activated FXa via a "slow-tight binding mechanism", i.e. rapid formation of a loose FXa-TFPI complex that then slowly isomerizes to a tight FXa-TFPI* complex. Subsequent inhibition of FVIIa is facilitated by the presence of tissue factor (TF) and FXa, which together rapidly and efficiently form a quaternary FXa-TFPI-TF-FVIIa complex in which the activity of FXa and FVIIa are inhibited. TFPI consists of 3 Kunitz-type protease inhibitor (KPI) domains in a tandem arrangement; The K1 domain of TFPI has been shown to bind and inhibit FVIIa while the K2 domain similarly inhibits FXa. Small peptide blocking inhibition of FXa and TF-FVIIa by TFPI shows that domain K1 is not only important for FVIIa inhibition but also for FXa inhibition, i.e. for the transition of the loose to the tight FXa-TFPI complex. The structure of the K1 domain is similar to those of other Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22613    4 CAFKADDGPCKAIMKRFFFNIFTRQCEEFIYGGCEGNENRFETLEECKKTC 54

Kunitz-type domain from the alpha3 chain of human type VI collagen, and similar proteins; This model includes the Kunitz-type domain from the alpha3 chain of type VI collagen (collagen alpha 3(VI) chain), encoded by COL6A3 gene. Collagen VI is a widely expressed member of the triple helix-containing protein superfamily of collagens and forms beaded microfibrils that anchor large interstitial structures. Immediately after fibril formation, the Kunitz domain can be cleaved off. Mutations in the alpha1, alpha2, and alpha3 chains of collagen VI cause myopathies ranging from the severe Ullrich congenital muscular dystrophy to the milder Bethlem myopathy, including intermediate forms. Early onset isolated dystonia, a neurological disease, has been shown to be caused by mutations in the alpha3 chain. Findings also indicated potential associations between COL6A3 polymorphisms and lung cancer risk. This domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22629    2 ICKLPKDEGTCRDFVLKWYYDPETKSCARFWYGGCGGNENRFDSQEECEKVC 53

Drosophila melanogaster Kunitz domain 1, Manduca sexta lacunin Kunitz domain 1, and simialr proteins; This model includes Drosophila melanogaster Kunitz domain 1 of papilin and Manduca sexta Kunitz domain 1 of lacunin, and similar proteins. D. melanogaster papilin is an essential extracellular matrix (ECM) protein that influences cell rearrangements. It may act by modulating metalloproteinase action during organogenesis and is able to non-competitively inhibit procollagen N-proteinase, an ADAMTS metalloproteinase. M. sexta lacunin is a large multidomain ECM containing several domains including several Kunitz-type protease inhibitors, thrombospondin type I, immunoglobulin-like and others. It exerts multiple effects on a variety of cell behaviors associated with the complex phenomenon of epithelial morphogenesis. These domains are similar to Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22639    1 CSLPKDRGPCRNYTVKWYFDMAYGGCSRFWYGGCGGNGNRFDTEEECKAVC 51

second Kunitz domain of WAP, Kazal, immunoglobulin, Kunitz and NTR domain-containing proteins; This subfamily includes WAP, Kazal, immunoglobulin, Kunitz and NTR domain-containing protein 1 (WFIKKN1, WFKN1), WFIKKN2 (WFKN2), and similar proteins. WFIKKN proteins are protease inhibitors that contain two distinct Kunitz-type protease inhibitor domains. They may have serine protease- and metalloprotease-inhibitor activity. This model represents the second Kunitz (KU2) domain, which has been shown to inhibit trypsin, but not chymotrypsin, elastase, plasmin, pancreatic kallikrein, lung tryptase, plasma kallikrein, thrombin, urokinase or tissue plasminogen activator. However, the inhibition constant of this domain for bovine trypsin is about five orders of magnitudes lower than that of bovine pancreatic trypsin inhibitor (BPTI) for trypsin. This could be due to unfavorable side-chain conformation of a tryptophan at P2' site which is incompatible with a trypsin complex; typical trypsin inhibitors of the Kunitz family feature a tyrosine residue or other less bulky residues at this site. The structure of KU2 is similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22606    1 ICSLPAVQGPCKAWEPRWAYNSLLKQCQSFVYGGCEGNENNFESKEACEDAC 52

first Kunitz domain of Rhipicephalus microplus boophilin and similar proteins; This group includes venom serine protease inhibitors such as Rhipicephalus microplus and Ixodes scapularis boofilin, among others. Boophilin prevents blood clot formation to allow successful feeding and digestion through its inhibition activity of thrombin and other host anticoagulating factors like kallikrein, coagulation factor VII, or plasmin; it interacts with the host thrombin and trypsin. The structures of these domains are similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds. Rhipicephalus microplus boophilin contains two Kunitz domains; this model represents the first repeat.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 528508507 313 AVCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:cd22599    4 GICRLPADEGICRALIPRFYFNTETGQCTEFIYGGCGGNENNFETIEECEKACG 57

first Kunitz domain of Carboxypeptidase Inhibitor SmCI and similar domains; This group includes Sabellastarte magnifica carboxypeptidase inhibitor (SmCI), a tri-domain BPTI-Kunitz inhibitor capable of inhibiting serine proteases and A-like metallocarboxypeptidases. While the BPTI-Kunitz family of proteins includes voltage gated channel blockers and inhibitors of serine proteases, SmCI is the only BPTI-Kunitz protein capable of inhibiting metallocarboxypeptidases. Binding studies show that SmCI is able to bind three trypsin molecules under saturating conditions, but only one elastase interacts with the inhibitor. Additionally, SmCI can bind serine proteases and carboxypeptidases at the same time (at least in the ratio 1:1:1), thus becoming the first protease inhibitor that simultaneously blocks these two mechanistic classes of enzymes. This model contains the first Kunitz domain of SmCI, which has a structure similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|...
gi 528508507 313 AVCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22601    2 DVCDLPADRGPCTAYIPRWFYNKTTKKCEKFVYGGCQGNKNRFETKDDCLANC 54

Kunitz domain 2 (KD2) of tissue factor pathway inhibitor 2 (TFPI2) and similar proteins; This model represents the Kunitz-type domain 2 (KD2) of tissue factor pathway inhibitor 2 (TFPI2 or TFPI-2) and similar proteins. TFPI2 exhibits inhibitory activity primarily toward trypsin, plasmin, and factor VIIa (FVIIa)/tissue factor (TF) via its KD1. It is believed to be the major inhibitor of plasmin in the extracellular matrix (ECM) but has little inhibitory activity toward urokinase-type plasminogen activator, tissue-type plasminogen activator, or thrombin. While TFPI2 specifically inhibits the proteases via the P1 arginine residue in KD1, domains KD2 and KD3 appear to have no discernible inhibitory activity and may serve to bind to nearby proteins to localize TFPI2 in the ECM. This domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22617    3 VCREVPDEGPCRALITRYFYNMTSMRCEEFTYGGCYGNGNNFRDKSSCISAC 54

Kunitz-type domain from the alpha6 chain of human type VI collagen, and similar proteins; This model includes the Kunitz-type domain from the alpha6 chain of type VI collagen (collagen alpha 6(VI) chain), encoded by COL6A6 gene, and similar proteins. Collagen VI is a widely expressed member of the triple helix-containing protein superfamily of collagens and forms beaded microfibrils that anchor large interstitial structures. Immediately after fibril formation, the Kunitz domain can be cleaved off. This domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|..
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22630    2 ACSLDQDEGECQNYVLKWYYDQEQKECSQFWYGGCGGNKNRFETQEECEALC 53

Kunitz-type actitoxins such as Anemonia viridis U-actitoxin-Avd3l, and similar proteins; This model includes the Kunitz-type actitoxins such as Anemonia viridis U-actitoxin-Avd3l (also called U-AITX-Avd3l or AsKC9), Anthopleura elegantissima KappaPI-actitoxin-Ael3a (also called KappaPI-AITX-Ael3a or Kunitz-type serine protease inhibitor APEKTx1) and Anthopleura aff. xanthogrammica PI-actitoxin-Axm2b (also called PI-AITX-Axm2b or Kunitz-type proteinase inhibitor AXPI-II). U-AITX-Avd3l and KappaPI-AITX-Ael3a are dual-function toxins that inhibit both the serine protease trypsin and voltage-gated potassium channels Kv1.2/KCNA2. These proteins are similar to Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|....*
gi 528508507 311 VEAVCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22633    1 INSICLLPKDVGGCRARFPRYYYNSSTRRCEKFRYGGCGGNANNFHTLEECEKVC 55

Stichodactyla helianthus Kunitz inhibitor protein ShPI-1, Heteractis crispa protease inhibitor stichotoxin-Hcr2e, and similar proteins; This model includes Kunitz inhibitor protein ShPI-1, the major protease inhibitor from the sea anemone Stichodactyla helianthus, as well as protease inhibitor stichotoxin-Hcr2e (also called PI- stichotoxin-Hcr2e, PI-SHTX-Hcr2e, or Kunitz-type serine protease inhibitor InhVJ) and HCRG1 from Heteractis crispa. ShPI-1 has an unusually broad specificity toward several serine proteases, including trypsin, chymotrypsin, human neutrophil elastase, kallikrein and plasmin, and can also bind aspartic and cysteine proteases, such as pepsin and papain, respectively. PI-SHTX-Hcr2e and HCRG1 inhibit trypsin and chymotrypsin, but do not inhibit the serine proteases plasmin, thrombin, kallikrein, the cysteine proteinase papain, and the aspartic protease pepsin. The structures of these domains are similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|...
gi 528508507 314 VCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:cd22618    1 ICSEPKVVGPCKAYFPRFYFDSETGKCTPFIYGGCGGNGNNFETLHACRAICR 53

Drosophila melanogaster Kunitz domains 5, 6, 7, and Caenorhabditis elegans Kunitz domain 5 of papilin, and similar domains; This model includes Kunitz domains from papilins with multiple Kunitz domains, such as Drosophila melanogaster Kunitz domains 5, 6, 7, and Caenorhabditis elegans Kunitz domain 5 of papilin, among others. Papilins are essential for embryonic development. D. melanogaster papilin is an essential extracellular matrix (ECM) protein that influences cell rearrangements. It may act by modulating metalloproteinases action during organogenesis and is able to non-competitively inhibit procollagen N-proteinase, an ADAMTS metalloproteinase. C. elegans papilin (also called abnormal cell migration protein 6) mig-6 encodes long (MIG-6L) and short (MIG-6S) isoforms of the extracellular matrix protein papilin, each required for distinct aspects of distal tip cell (DTC) migration and both isoforms have an N-terminal papilin cassette, lagrin repeats and six C-terminal Kunitz-type serine proteinase inhibitory domains. It plays a role in embryogenesis, the second phase of distal cell tip migration and is required for distribution of the metalloproteinase, mig-17, during organogenesis. These domains are similar to Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22637    1 CDQPKDTGPCDNWVLKWYYDSKKGSCRQFYYGGCGGNDNRFDTEEECEARC 51

Kunitz protease inhibitor (KPI) domain 2 (KPI-2 or K2) of tissue factor pathway inhibitor (TFPI); This model represents the second Kunitz-type domain (K2 or KPI-2) of tissue factor pathway inhibitor (TFPI or TFPI1), also known as extrinsic pathway inhibitor (EPI) or lipoprotein-associated coagulation inhibitor (LACI). TFPI down-regulates the extrinsic coagulation pathway via inhibition of activated factor X (FXa or Xa) and FVIIa (VIIa). It inhibits activated FXa via a "slow-tight binding mechanism", i.e. rapid formation of a loose FXa-TFPI complex that then slowly isomerizes to a tight FXa-TFPI* complex. Subsequent inhibition of FVIIa is facilitated by the presence of tissue factor (TF) and FXa, which together rapidly and efficiently form a quaternary FXa-TFPI-TF-FVIIa complex in which the activity of FXa and FVIIa are inhibited. TFPI consists of 3 Kunitz-type protease inhibitor (KPI) domains in a tandem arrangement; the K2 domain is exposed on functionally active TFPI pools in circulation in blood, in platelets, and attached to the endothelium. While the K1 (or KPI-1) domain of TFPI has been shown to bind and inhibit FVIIa, the K2 domain inhibits FXa by binding directly to the active site and forming a FXa:TFPI complex. A close interaction between the TFPI K2 domain and the FXa active site is essential for the FXa inhibitory action of TFPI and for the formation of an inactive TF/FVIIa/FXa/TFPI complex which then prevents FXa generation. Thus, blockage of K2 would prevent TFPI binding to both FXa and FVIIa/TF, and fully abolish TFPI inhibition of the coagulation cascade. The structure of the K2 domain is similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22614    5 CFLEEDPGICRGLITRYFYNNQSKQCERFKYGGCLGNQNNFESLEECQNTC 55

Kunitz-type domain from the alpha6 chain of fish type VI collagen, and similar proteins; This model includes the Kunitz-type domain from the alpha6 chain of type VI collagen (collagen alpha 6(VI) chain) and similar proteins. Collagen VI is a widely expressed member of the triple helix-containing protein superfamily of collagens and forms beaded microfibrils that anchor large interstitial structures. Immediately after fibril formation, the Kunitz domain can be cleaved off. This domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22631    1 CLLGQDAGSCQNYTMMWFFDSKQGRCSRFWYGGCGGNANRFETQEECENLC 51

conkunitzin-S1 and -S2, and similar proteins; This model includes Kunitz-type conkunitzin-S1 (Cs1) and -S2 (Cs2). Conkunitzins are pore-modulating toxins that block voltage-dependent potassium channels (Kvs) by exploiting inherent slow inactivation to block K+ channels. Cs1 binds to the channel turrets and disrupts the structural water hydrogen-bonding network, exposing the peripheral water pockets of ion channels and triggering an asymmetric collapse of the pore. Conus bullatus conkunitzin-B1, expressed in the venom duct, specifically blocks voltage-activated potassium channels (Kv) of the Shaker family. Members of this subfamily contain 2 disulfide bonds instead of the 3 present in most Kunitz domain proteins.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22593    1 CSLPLDEGSGNSSLTRWYYDPKKGQCKPFTYKGKGGNENNFLTKEDCEETC 51

Kunitz protease inhibitor (KPI) domain 3 (KPI-3 or K3) of tissue factor pathway inhibitor (TFPI) and TFPI2, and similar proteins; This model represents the third Kunitz-type domain (K3 or KPI-3) of tissue factor pathway inhibitor (TFPI or TFPI1), also known as extrinsic pathway inhibitor (EPI) or lipoprotein-associated coagulation inhibitor (LACI), and of TFPI2 (or TFPI-2). TFPI1 down-regulates the extrinsic coagulation pathway via inhibition of activated factor X (FXa or Xa) and FVIIa (VIIa). It inhibits activated FXa via a "slow-tight binding mechanism", i.e. rapid formation of a loose FXa-TFPI1 complex that then slowly isomerizes to a tight FXa-TFPI1* complex. Subsequent inhibition of FVIIa is facilitated by the presence of tissue factor (TF) and FXa, which together rapidly and efficiently form a quaternary FXa-TFPI1-TF-FVIIa complex in which the activity of FXa and FVIIa are inhibited. TFPI1 consists of 3 Kunitz-type protease inhibitor (KPI) domains in a tandem arrangement; while the K1 domain of TFPI has been shown to bind and inhibit FVIIa and the K2 domain similarly inhibits FXa, the K3 domain has no known inhibitory function. However, Protein S, which functions as a cofactor for TFPI to efficiently enhance TFPI inhibition of FXa and FXa activated TF-VIIa, is dependent on direct interactions with two important residues within K3, a Glutamate and an Arginine. This model also includes TFPI2 Kunitz domain 3 (KD3). TFPI2 exhibits inhibitory activity primarily toward trypsin, plasmin, and factor VIIa (FVIIa)/tissue factor (TF) via its KD1. It is believed to be the major inhibitor of plasmin in the extracellular matrix (ECM) but has little inhibitory activity toward urokinase-type plasminogen activator, tissue-type plasminogen activator, or thrombin. While TFPI2 specifically inhibits the proteases via the P1 arginine residue in KD1, domains KD2 and KD3 appear to have no discernible inhibitory activity and may serve to bind to nearby proteins to localize TFPI2 in the ECM. The structure of this domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22615    4 CLSPKDEGLCSASVTRYYYNSATKTCEPFNYTGCGGNNNNFTSKKDCLRVC 54

first Kunitz domain of WAP, Kazal, immunoglobulin, Kunitz and NTR domain-containing proteins; This subfamily includes WAP, Kazal, immunoglobulin, Kunitz and NTR domain-containing protein 1 (WFIKKN1, WFKN1), WFIKKN2 (WFKN2), and similar proteins. WFIKKN proteins are protease inhibitors that contain two distinct Kunitz-type protease inhibitor domains. They may have serine protease- and metalloprotease-inhibitor activity. This model represents the first Kunitz domain that is similar to Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor) that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22605    2 CLKEPDREDCGEEQVRWYFDAKRGNCFTFTYGGCDGNRNHFETYEECRLAC 52

first Kunitz domain of bikunin and similar proteins; This subfamily includes the N-terminal domain of bikunin (also known as inter-alpha-trypsin inhibitor light chain (ITI-LC) or urinary trypsin inhibitor), a plasma protease inhibitor, that is associated with inflammation and stabilizes the extracellular matrix. It is encoded together with alpha-1-microglobulin (A1M) by an alpha-1-microglobulin/bikunin precursor (AMBP) gene that is tightly controlled by several hepatocyte-enriched nuclear (HEN) factors, and cleaved by a furin-like protease that releases the two mature molecules. Bikunin is a Kunitz-type serine protease inhibitor, found in vertebrate serum and urine, modified by a chondroitin sulfate (CS) chain. The structures of these toxins are similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds. Bikunin contains two Kunitz domains; this model represents the first repeat.

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gi 528508507 313 AVCSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVCK 366
Cdd:cd22596    1 DSCKLPPDAGPCFGMIQRYFYNSSSMACQTFNYGGCLGNQNNFVTEKECLQTCR 54

Kunitz-type domain from the alpha1 chain of type VII collagen, and similar proteins; This model includes the Kunitz-type domain from the alpha1 chain of type VII collagen (collagen alpha-1(VII) chain also called long-chain collagen or LC collagen) and similar proteins. LC collagen, encoded by the COL7A1 gene, is a stratified squamous epithelial basement membrane protein that forms anchoring fibrils which may contribute to epithelial basement membrane organization and adherence by interacting with extracellular matrix (ECM) proteins such as type IV collagen. So far, over 800 COL7A1 mutations have been reported, including missense, nonsense, splicing, insertion, and deletion mutations which to varying degrees leads to deficiency of type VII collagen. Epidermolysis bullosa acquisita (EBA) is an autoimmune acquired blistering skin disease resulting from autoantibodies to type VII collagen. The COL7A1 protein contains a Kunitz domain, the deactivation of which induces tumorigenesis. This domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), that shows an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22627    3 CLLPMDEGSCSDYTLLWYYHQKAGECRPFVYGGCGGNANRFSSKEDCELRC 53

Kunitz-type serine protease inhibitor subunit of beta 2-bungarotoxin, and similar proteins; This model includes the Kunitz inhibitor subunit of beta 2-bungarotoxin, a presynaptic neurotoxin of the Bungarus multicinctus venom. Beta-bungarotoxin is a heterodimeric neurotoxin consisting of a phospholipase subunit linked by a disulfide bond to the Kunitz protease inhibitor subunit; the latter subunit is homologous to venom basic protease inhibitors but has no protease inhibitor activity and is non-toxic. The beta-bungarotoxin Kunitz subunit serves to guide the toxin to its site of action on the presynaptic membrane by virtue of a high-affinity interaction with a specific subclass of voltage-sensitive potassium channels. This subfamily also includes Kunitz-type serine protease inhibitor homolog beta-bungarotoxin B1 chain and protease inhibitor-like protein 1 (PILP-1). The B1 chain also has no protease inhibitor activity but blocks voltage-gated potassium channels, while PILP-1 inhibits trypsin. The structures of these domains are similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*....|....*....|.
gi 528508507 315 CSLEAETGPCRASMPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22619    7 CDKPPDTKRCKRVVRAFYYNPSAKTCLQFVYGGCNGNGNHFKSKALCRCHC 57

Kunitz-type domain 1 (K1) of Ixolaris, and similar proteins; This model includes the first Kunitz-type domain (K1) of ixolaris from the venomous organism Conus striatus. Ixolaris is a potent tick salivary anticoagulant that binds coagulation factor Xa (FXa) and zymogen FX, and forms a quaternary tissue factor (TF)/FVIIa/FX(a)/Ixolaris inhibitory complex. It blocks TF-induced coagulation and PAR2 (proteinase-activated receptor 2) signaling, and prevents thrombosis, tumor growth, and immune activation. Ixolaris consists of 2 Kunitz domains (K1 and K2), both of which recognize the heparin-binding (pro)exosite (HBE) on FX. While K2 is an extraordinarily dynamic domain that encompasses several residues involved in FX binding, K1 domain keeps as a rigid platform supporting the conformational dynamic of the K2 domain, forming a salt bridge with FXa. The structure of this domain is similar to that of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.

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                 ....*....|....*....|....*....|....*...
gi 528508507 328 MPRWHFDMQQRKCVRFIYGGCAGNRNNFDSEEYCMVVC 365
Cdd:cd22625   16 TKRYGYNKKTQQCEEFLGTECGGGGNSFEEAKECWSSC 53