The S26 Type I signal peptidase (SPase; LepB; leader peptidase B; leader peptidase I; EC 3.4.21.89) family members are essential membrane-bound serine proteases that function to cleave the amino-terminal signal peptide extension from proteins that are translocated across biological membranes. The bacterial signal peptidase I, which is the most intensively studied, has two N-terminal transmembrane segments inserted in the plasma membrane and a hydrophilic, C-terminal catalytic region that is located in the periplasmic space. Although the bacterial signal peptidase I is monomeric, signal peptidases of eukaryotic cells commonly function as oligomeric complexes containing two divergent copies of the catalytic monomer. These are the IMP1 and IMP2 signal peptidases of the mitochondrial inner membrane that remove leader peptides from nuclear- and mitochondrial-encoded proteins. Also, two components of the endoplasmic reticulum signal peptidase in mammals (18-kDa and 21-kDa) belong to this family and they process many proteins that enter the ER for retention or for export to the Golgi apparatus, secretory vesicles, plasma membranes or vacuole. An atypical member of the S26 SPase type I family is the TraF peptidase which has the remarkable activity of producing a cyclic protein of the Pseudomonas pilin system. The type I signal peptidases are unique serine proteases that utilize a serine/lysine catalytic dyad mechanism in place of the classical serine/histidine/aspartic acid catalytic triad mechanism.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184  33 VVMCSGPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGlegdkilttspsdffkshsyvpmgh 112
Cdd:cd06530    2 PVVVPGGSMEPTLQPGDLVLVNKLSYGFREPKRGDVVVFKSPGDPGKPIIKRVIG------------------------- 56

                         90       100
                 ....*....|....*....|....*....
gi 747019184 113 VWLEGDNLQNSTDSRCYGPIPYGLIRGRI 141
Cdd:cd06530   57 YFVLGDNRNNSLDSRYWGPVPEDDIVGKV 85

The S26 Type I signal peptidase (SPase; LepB; leader peptidase B; leader peptidase I; EC 3.4.21.89) family members are essential membrane-bound serine proteases that function to cleave the amino-terminal signal peptide extension from proteins that are translocated across biological membranes. The bacterial signal peptidase I, which is the most intensively studied, has two N-terminal transmembrane segments inserted in the plasma membrane and a hydrophilic, C-terminal catalytic region that is located in the periplasmic space. Although the bacterial signal peptidase I is monomeric, signal peptidases of eukaryotic cells commonly function as oligomeric complexes containing two divergent copies of the catalytic monomer. These are the IMP1 and IMP2 signal peptidases of the mitochondrial inner membrane that remove leader peptides from nuclear- and mitochondrial-encoded proteins. Also, two components of the endoplasmic reticulum signal peptidase in mammals (18-kDa and 21-kDa) belong to this family and they process many proteins that enter the ER for retention or for export to the Golgi apparatus, secretory vesicles, plasma membranes or vacuole. An atypical member of the S26 SPase type I family is the TraF peptidase which has the remarkable activity of producing a cyclic protein of the Pseudomonas pilin system. The type I signal peptidases are unique serine proteases that utilize a serine/lysine catalytic dyad mechanism in place of the classical serine/histidine/aspartic acid catalytic triad mechanism.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184  33 VVMCSGPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGlegdkilttspsdffkshsyvpmgh 112
Cdd:cd06530    2 PVVVPGGSMEPTLQPGDLVLVNKLSYGFREPKRGDVVVFKSPGDPGKPIIKRVIG------------------------- 56

                         90       100
                 ....*....|....*....|....*....
gi 747019184 113 VWLEGDNLQNSTDSRCYGPIPYGLIRGRI 141
Cdd:cd06530   57 YFVLGDNRNNSLDSRYWGPVPEDDIVGKV 85

Signal peptidase, peptidase S26; This is a family of membrane signal serine endopeptidases which function in the processing of newly-synthesized secreted proteins. Peptidase S26 removes the hydrophobic, N-terminal, signal peptides as proteins are translocated across membranes. The active site residues take the form of a catalytic dyad that is Ser, Lys in subfamily S26A; the Ser is the nucleophile in catalysis, and the Lys is the general base.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184   38 GPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGLEGDKI----------------------LT 95
Cdd:pfam10502  30 GGSMSPTLPIGDYLIVNKFSYGLGEPKRGDIVVFRPPEGPGVPLIKRVIGLPGDRVeykddqlyingkpvgepyladrKG 109

                          90       100       110       120       130
                  ....*....|....*....|....*....|....*....|....*....|...
gi 747019184   96 TSPSDF--FKSHSYVPMGHVWLEGDNLQNSTDSRCYGPIPYGLIRGRIFFKIW 146
Cdd:pfam10502 110 RPTFDLppWQGCRVVPEGEYFVMGDNRDNSLDSRYFGFVPASNIVGRAVFPVW 162

signal peptidase I;

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 747019184  37 SGpSMEPTIQNSDIVFAENLSrhfYGI---------------QRGDIVIAKSPSDPKSNICKRVIGLEGDKI 93
Cdd:PRK10861  89 SG-SMMPTLLIGDFILVEKFA---YGIkdpitqttlietghpKRGDIVVFKYPEDPKLDYIKRVVGLPGDKV 156

The S26 Type I signal peptidase (SPase; LepB; leader peptidase B; leader peptidase I; EC 3.4.21.89) family members are essential membrane-bound serine proteases that function to cleave the amino-terminal signal peptide extension from proteins that are translocated across biological membranes. The bacterial signal peptidase I, which is the most intensively studied, has two N-terminal transmembrane segments inserted in the plasma membrane and a hydrophilic, C-terminal catalytic region that is located in the periplasmic space. Although the bacterial signal peptidase I is monomeric, signal peptidases of eukaryotic cells commonly function as oligomeric complexes containing two divergent copies of the catalytic monomer. These are the IMP1 and IMP2 signal peptidases of the mitochondrial inner membrane that remove leader peptides from nuclear- and mitochondrial-encoded proteins. Also, two components of the endoplasmic reticulum signal peptidase in mammals (18-kDa and 21-kDa) belong to this family and they process many proteins that enter the ER for retention or for export to the Golgi apparatus, secretory vesicles, plasma membranes or vacuole. An atypical member of the S26 SPase type I family is the TraF peptidase which has the remarkable activity of producing a cyclic protein of the Pseudomonas pilin system. The type I signal peptidases are unique serine proteases that utilize a serine/lysine catalytic dyad mechanism in place of the classical serine/histidine/aspartic acid catalytic triad mechanism.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184  33 VVMCSGPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGlegdkilttspsdffkshsyvpmgh 112
Cdd:cd06530    2 PVVVPGGSMEPTLQPGDLVLVNKLSYGFREPKRGDVVVFKSPGDPGKPIIKRVIG------------------------- 56

                         90       100
                 ....*....|....*....|....*....
gi 747019184 113 VWLEGDNLQNSTDSRCYGPIPYGLIRGRI 141
Cdd:cd06530   57 YFVLGDNRNNSLDSRYWGPVPEDDIVGKV 85

Signal peptidase, peptidase S26; This is a family of membrane signal serine endopeptidases which function in the processing of newly-synthesized secreted proteins. Peptidase S26 removes the hydrophobic, N-terminal, signal peptides as proteins are translocated across membranes. The active site residues take the form of a catalytic dyad that is Ser, Lys in subfamily S26A; the Ser is the nucleophile in catalysis, and the Lys is the general base.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184   38 GPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGLEGDKI----------------------LT 95
Cdd:pfam10502  30 GGSMSPTLPIGDYLIVNKFSYGLGEPKRGDIVVFRPPEGPGVPLIKRVIGLPGDRVeykddqlyingkpvgepyladrKG 109

                          90       100       110       120       130
                  ....*....|....*....|....*....|....*....|....*....|...
gi 747019184   96 TSPSDF--FKSHSYVPMGHVWLEGDNLQNSTDSRCYGPIPYGLIRGRIFFKIW 146
Cdd:pfam10502 110 RPTFDLppWQGCRVVPEGEYFVMGDNRDNSLDSRYFGFVPASNIVGRAVFPVW 162

Signal peptidase I [Intracellular trafficking, secretion, and vesicular transport];

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*.
gi 747019184  38 GPSMEPTIQNSDIVFAENLSRHFYGIQRGDIVIAKSPSDPKSNICKRVIGLEGDKI 93
Cdd:COG0681   40 SGSMEPTLLVGDRLLVNKLSYGFGEPKRGDIVVFKYPEDPSKDYIKRVIGLPGDTV 95

Type IV secretory pathway, protease TraF [Posttranslational modification, protein turnover, chaperones, Intracellular trafficking, secretion, and vesicular transport];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184  65 RGDIVIAKSPSDPKSNIC---------KRVIGLEGDKI---------------------LTTSPSDFFKSHSYVPMGHVW 114
Cdd:COG4959    1 RGDLVAFRPPEPLAAERGylprgvpliKRVAALPGDTVcikggqvyingkpvaealerdRAGRPLPVWQGCGVVPEGEYF 80

                         90       100       110
                 ....*....|....*....|....*....|...
gi 747019184 115 LEGDNLQNSTDSRCYGPIPYGLIRGRIFFKIWP 147
Cdd:COG4959   81 LLGDNRPNSFDSRYFGPVPRSQIIGRAVPLWTP 113

signal peptidase I, archaeal type; This model represents signal peptidase I from most archaea, a subunit of the eukaryotic endoplasmic reticulum signal peptidase I complex, and an apparent signal peptidase I from a small number of bacteria. It is related to but does not overlap in hits with TIGR02227, the bacterial and mitochondrial signal peptidase I.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....*.
gi 747019184   32 GVVMCSGPSMEPTIQNSDIVFAEnlSRHFYGIQRGDIVIAKSPSDPKSnICKRVIG 87
Cdd:TIGR02228  32 PVVVVLSGSMEPTFNTGDLILVT--GADPNDIQVGDVITYKSPGFNTP-VTHRVIE 84

Peptidase S24 LexA-like proteins are involved in the SOS response leading to the repair of single-stranded DNA within the bacterial cell. This family includes: the lambda repressor CI/C2 family and related bacterial prophage repressor proteins; LexA (EC 3.4.21.88), the repressor of genes in the cellular SOS response to DNA damage; MucA and the related UmuD proteins, which are lesion-bypass DNA polymerases, induced in response to mitogenic DNA damage; RulA, a component of the rulAB locus that confers resistance to UV, and RuvA, which is a component of the RuvABC resolvasome that catalyzes the resolution of Holliday junctions that arise during genetic recombination and DNA repair. The LexA-like proteins contain two-domains: an N-terminal DNA binding domain and a C-terminal domain (CTD) that provides LexA dimerization as well as cleavage activity. They undergo autolysis, cleaving at an Ala-Gly or a Cys-Gly bond, separating the DNA-binding domain from the rest of the protein. In the presence of single-stranded DNA, the LexA, UmuD and MucA proteins interact with RecA, activating self cleavage, thus either derepressing transcription in the case of LexA or activating the lesion-bypass polymerase in the case of UmuD and MucA. The LexA proteins are serine proteases that carry out catalysis using a serine/lysine dyad instead of the prototypical serine/histidine/aspartic acid triad found in most serine proteases. LexA sequence homologs are found in almost all of the bacterial genomes sequenced to date, covering a large number of phyla, suggesting both, an ancient origin and a widespread distribution of lexA and the SOS response.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 747019184  33 VVMCSGPSMEPTIQNSDIVFAeNLSRHfygIQRGDIVIAKSPSDPksnICKRVIglegdkilttspsdffkshsYVPMGH 112
Cdd:cd06529    2 ALRVKGDSMEPTIPDGDLVLV-DPSDT---PRDGDIVVARLDGEL---TVKRLQ--------------------RRGGGR 54

                         90       100       110
                 ....*....|....*....|....*....|....
gi 747019184 113 VWLEGDNLQnstdsrcYGPIPYGLIRGRIFFKIW 146
Cdd:cd06529   55 LRLISDNPA-------YPPIEIDEEELEIVGVVG 81