Hsp20/alpha crystallin family; Not only do small heat-shock-proteins occur in eukaryotes and prokaryotes but they have also now been shown to occur in cyanobacterial phages as well as their bacterial hosts.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 635552605   24 EWKDQPEATILNIDLTGFAKEQMKVTYVHSSKMIRVTGERPLANRKWSR-------FNEVFTVPQNCLVDKIHGSFKNNV 96
Cdd:pfam00011   1 DIKEDEDAFEVRLDVPGFKPEELKVKVEDNRLLVKGEHEEEKEDDHGLRsersygsFSRKFTLPENADPDKVKASLKDGV 80

                  ....*..
gi 635552605   97 LTITMPK 103
Cdd:pfam00011  81 LTVTVPK 87

Alpha crystallin domain (ACD) found in Saccharomyces cerevisiae (Sc) small heat shock protein (Hsp)26 and similar proteins. sHsps are molecular chaperones that suppress protein aggregation and protect against cell stress, and are generally active as large oligomers consisting of multiple subunits. ScHsp26 is temperature-regulated, it switches from an inactive to a chaperone-active form upon elevation in temperature. It associates into large 24-mers storage forms which upon heat shock disassociate into dimers. These dimers initiate the interaction with non-native substrate proteins and re-assemble into large globular assemblies having one monomer of substrate bound per dimer. This group also contains Arabidopsis thaliana (Ath) Hsp15.7, a peroxisomal matrix protein which can complement the morphological phenotype of S. cerevisiae mutants deficient in Hsps26. AthHsp15.7 is minimally expressed under normal conditions and is strongly induced by heat and oxidative stress. Also belonging to this group is wheat HSP16.9 which differs in quaternary structure from the shell-type particles of ScHsp26, it assembles as a dodecameric double disc, with each disc organized as a trimer of dimers.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 635552605  25 WKDQPEATILNIDLTGFAKEQMKVtYVHSSKMIRVTGER----PLANRKW-------SRFNEVFTVPQNCLVDKIHGSFK 93
Cdd:cd06472    4 WKETPEAHVFKADVPGVKKEDVKV-EVEDGRVLRISGERkkeeEKKGDDWhrverssGRFVRRFRLPENADADEVKAFLE 82

                         90
                 ....*....|
gi 635552605  94 NNVLTITMPK 103
Cdd:cd06472   83 NGVLTVTVPK 92

This domain family includes the alpha-crystallin domain (ACD) of alpha-crystallin-type small heat shock proteins (sHsps) and a similar domain found in p23-like proteins. sHsps are small stress induced proteins with monomeric masses between 12 -43 kDa, whose common feature is this ACD. sHsps are generally active as large oligomers consisting of multiple subunits, and are believed to be ATP-independent chaperones that prevent aggregation and are important in refolding in combination with other Hsps. p23 is a cochaperone of the Hsp90 chaperoning pathway. It binds Hsp90 and participates in the folding of a number of Hsp90 clients including the progesterone receptor. p23 also has a passive chaperoning activity. p23 in addition may act as the cytosolic prostaglandin E2 synthase. Included in this family is the p23-like C-terminal CHORD-SGT1 (CS) domain of suppressor of G2 allele of Skp1 (Sgt1) and the p23-like domains of human butyrate-induced transcript 1 (hB-ind1), NUD (nuclear distribution) C, Melusin, and NAD(P)H cytochrome b5 (NCB5) oxidoreductase (OR).

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 635552605  25 WKDQPEATILNIDLTGFAKEQMKVTYvhSSKMIRVTGERPLAN---RKWSRFNEVFTVPQNCLVDKIHGSFKNNVLTITM 101
Cdd:cd00298    1 WYQTDDEVVVTVDLPGVKKEDIKVEV--EDNVLTISGKREEEEereRSYGEFERSFELPEDVDPEKSKASLENGVLEITL 78

                 ..
gi 635552605 102 PK 103
Cdd:cd00298   79 PK 80

Group of bacterial proteins containing an alpha crystallin domain (ACD) similar to Lactobacillus plantarum (Lp) small heat shock proteins (sHsp) HSP 18.5, HSP 18.55 and HSP 19.3. sHsps are molecular chaperones that suppress protein aggregation and protect against cell stress, and are generally active as large oligomers consisting of multiple subunits. Transcription of the genes encoding Lp HSP 18.5, 18.55 and 19.3 is regulated by a variety of stresses including heat, cold and ethanol. Early growing L. plantarum cells contain elevated levels of these mRNAs which rapidly fall of as the cells enter stationary phase. Also belonging to this group is Bifidobacterium breve (Bb) HSP20 and Oenococcus oenis (syn. Leuconostoc oenos) (Oo) HSP18. Transcription of the gene encoding BbHSP20 is strongly induced following heat or osmotic shock, and that of the gene encoding OoHSP18 following heat, ethanol or acid shock. OoHSP18 is peripherally associated with the cytoplasmic membrane.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 635552605  26 KDQPEATILNIDLTGFAKEQMKVTY---------VHSS---------KMIRvtgerplANRKWSRFNEVFTVPqNCLVDK 87
Cdd:cd06471    6 KETDDEYIVEADLPGFKKEDIKLDYkdgyltisaKRDEskdekdkkgNYIR-------RERYYGSFSRSFYLP-NVDEEE 77

                         90
                 ....*....|....*.
gi 635552605  88 IHGSFKNNVLTITMPK 103
Cdd:cd06471   78 IKAKYENGVLKITLPK 93