Trypsin-like serine protease
SMART accession number:SM00020
Description: Many of these are synthesised as inactive precursor zymogens that are cleaved during limited proteolysis to generate their active forms. A few, however, are active as single chain molecules, and others are inactive due to substitutions of the catalytic triad residues.
Interpro abstract (IPR001254):

In the MEROPS database peptidases and peptidase homologues are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry based on a common structural fold:

  • 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-, N-, 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.
  • Peptidase families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; N, asparagine; 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. In the case of the asparagine endopeptidases, the nucleophile is asparagine and all are self-processing endopeptidases.

In many instances the structural protein fold that characterises the clan or family may have lost its catalytic activity, yet retain its function in protein recognition and binding.

Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes [(PUBMED:7845208)]. They include a wide range of peptidase activity, including exopeptidase, endopeptidase, oligopeptidase and omega-peptidase activity. Many families of serine protease have been identified, these being grouped into clans on the basis of structural similarity and other functional evidence [(PUBMED:7845208)]. 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 [(PUBMED:7845208)].

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 [(PUBMED:7845208)]. The geometric orientations of the catalytic residues are similar between families, despite different protein folds [(PUBMED:7845208)]. 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) [(PUBMED:7845208), (PUBMED:8439290)].

This group of serine proteases belong to the MEROPS peptidase family S1 (chymotrypsin family, clan PA(S))and to peptidase family S6 (Hap serine peptidases).

The chymotrypsin family is almost totally confined to animals, although trypsin-like enzymes are found in actinomycetes of the genera Streptomyces and Saccharopolyspora, and in the fungus Fusarium oxysporum [(PUBMED:7845208)]. The enzymes are inherently secreted, being synthesised with a signal peptide that targets them to the secretory pathway. Animal enzymes are either secreted directly, packaged into vesicles for regulated secretion, or are retained in leukocyte granules [(PUBMED:7845208)].

The Hap family, 'Haemophilus adhesion and penetration', are proteins that play a role in the interaction with human epithelial cells. The serine protease activity is localized at the N-terminal domain, whereas the binding domain is in the C-terminal region.

GO process:proteolysis (GO:0006508)
GO function:serine-type endopeptidase activity (GO:0004252)
Family alignment:
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There are 12104 Tryp_SPc domains in 11834 proteins in SMART's nrdb database.

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