| Comment | This HMM describes a domain that occurs once in the major pilin of Streptococcus pyogenes, Spy0128, but in higher copy numbers in other streptococcal proteins. The domain occurs nine times in a surface-anchored protein of Bifidobacterium longum. All members of this family have LPXTG-type sortase target sequences. The S. pyogenes major pilin has been shown to undergo isopeptide bond cross-linking, mediated by sortases, that are critical to maintaining pilus structural integrity. One such Lys-to-Asn isopeptide bond is to a near-invariant Asn near the C-terminal end of this domain (column 81 of the seed alignment). A Glu in the S. pyogenes major pilin (column 25 of the seed alignment), invariant as Glu or Gln, is described as catalytic for isopeptide bond formation. |
