>TIGR00706 SppA_dom signal peptide peptidase SppA, 36K type; InterPro: IPR004635 Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes . They include a wide range of peptidase activity, including exopeptidase, endopeptidase, oligopeptidase and omega-peptidase activity. Over 20 families (denoted S1 - S66) of serine protease have been identified, these being grouped into clans on the basis of structural similarity and other functional evidence . Structures are known for members of the clans and the structures indicate that some appear to be totally unrelated, suggesting different evolutionary origins for the serine peptidases . Not withstanding their different evolutionary origins, there are similarities in the reaction mechanisms of several peptidases. Chymotrypsin, subtilisin and carboxypeptidase C have a catalytic triad of serine, aspartate and histidine in common: serine acts as a nucleophile, aspartate as an electrophile, and histidine as a base . The geometric orientations of the catalytic residues are similar between families, despite different protein folds . The linear arrangements of the catalytic residues commonly reflect clan relationships. For example the catalytic triad in the chymotrypsin clan (PA) is ordered HDS, but is ordered DHS in the subtilisin clan (SB) and SDH in the carboxypeptidase clan (SC) , . Peptidases are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry. Each clan is identified with two letters, the first representing the catalytic type of the families included in the clan (with the letter 'P' being used for a clan containing families of more than one of the catalytic types serine, threonine and cysteine). Some families cannot yet be assigned to clans, and when a formal assignment is required, such a family is described as belonging to clan A-, C-, M-, S-, T- or U-, according to the catalytic type. Some clans are divided into subclans because there is evidence of a very ancient divergence within the clan, for example MA(E), the gluzincins, and MA(M), the metzincins. Families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; S, serine; T, threonine; and U, unknown. The serine, threonine and cysteine peptidases utilise the amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic, glutamic and metallopeptidases, the nucleophile is an activated water molecule. This group of serine peptidases belong to MEROPS peptidase family S49 (protease IV family, clan S-). The predicted active site serine for members of this family occurs in a transmembrane domain. This group of sequences represent both long and short forms of the bacterial SppA and homologs found in the archaea and plants. Signal peptides of secretory proteins seem to serve at least two important biological functions. First, they are required for protein targeting to and translocation across membranes, such as the eubacterial plasma membrane and the endoplasmic reticular membrane of eukaryotes. Second, in addition to their role as determinants for protein targeting and translocation, certain signal peptides have a signaling function. During or shortly after pre-protein translocation, the signal peptide is removed by signal peptidases. The integral membrane protein, SppA (protease IV), of Escherichia coli was shown experimentally to degrade signal peptides. The member of this family from Bacillus subtilis has only been shown to be required for efficient processing of pre-proteins under conditions of hyper-secretion . ; GO: 0008233 peptidase activity, 0006508 proteolysis.

Probab=94.33  E-value=0.18  Score=32.01  Aligned_cols=137  Identities=23%  Similarity=0.242  Sum_probs=82.4

Q ss_pred             HHHCCCCCHHHHHHHHHHHHHHHHH-CCC-EEEEECCCCCCCCCCHHHHHHHHHHHHHHHHHH-HCCCCEEEEECCC-CC
Q ss_conf             0318535778999999999999862-896-899976888776521246777788999999998-6299889985676-42
Q gi|254780820|r  130 SFIGGSIGIAAGEAIVKSCERAIAE-KCP-LVMFTASGGARMQEGILSLMQLPRTTIAINMLK-DAGLPYIVVLTNP-TT  205 (284)
Q Consensus       130 ~F~GGSmG~~~geki~~a~e~A~~~-~~P-lI~~~~SGGaRMqEG~~sL~qMakt~~a~~~l~-~~~lP~I~vl~~p-t~  205 (284)
T Consensus        18 ~~~~~~Dg-~~~~~~~k~~~~~~~~~~~ka~~l~i~SPGG~V~-------~S~Eiy~~l~~~~k~~kkPVv~~~g~~aaS   89 (224)
T TIGR00706        18 SILLFSDG-VSPEDVLKKIKRIKDDKSIKALVLRIDSPGGTVV-------ASEEIYEKLKKLKKEAKKPVVASMGGVAAS   89 (224)
T ss_pred             CCCCCCCC-CCHHHHHHHHHHHHHCCCEEEEEEEEECCCCCCH-------HHHHHHHHHHHHHHHCCCEEEEEECCCCHH
T ss_conf             10125689-9756799998877408970069998637999752-------268999999863453088589983683226


Q ss_pred             CEEEEEECCCCCEEEEECCCEEECCCHHHHHHHHC-CCCCCCCHHHHHHHHCCCC-CEEECHHHHHHHHHHHHHH
Q ss_conf             01111201468525553142110232788787636-7788720215999968983-5373589999999999999
Q gi|254780820|r  206 GGVTASYAMLGDIHLAEPGAEIGFAGRRVIEQTVR-EKLPDGFQRSEYLVEHGMI-DRIVHRHDIPEVVSSLCKI  278 (284)
Q Consensus       206 GGv~AS~a~lgDiiiaep~a~igFaG~rVi~~t~~-~~lp~~fqtae~l~~~G~i-D~iv~r~~l~~~i~~ll~i  278 (284)
T Consensus        90 GGYYi--a~aa~~I~A~~~t~tGSIG--VIl~~~n~~~L~~k~GI~~~~iK~G~yKd~~~~~R~lt~eE~~~lQ~  160 (224)
T TIGR00706        90 GGYYI--AMAADEIVANPGTITGSIG--VILQGANVEKLLEKLGIEFEAIKSGEYKDIGSPTRELTPEERKILQS  160 (224)
T ss_pred             HHHHH--HHCCCEEEECCCCCEECHH--HHHHHHHHHHHHHHCCCEEEEEECCCCCCCCCCHHHHHHHHHHHHHH
T ss_conf             79999--8138824634774202037--55203579999986491565665166567898757762999999999