PROSITE documentation PDOC51109

G5 domain profile

The G5 domain (named after its conserved glycine residues) is a module of ~80 residues that is found in a variety of enzymes such as Streptococcal IgA peptidases and various glycosyl hydrolases in bacteria. It is found in one to seven copies in association with other domains, such as LysM, bacterial Ig-like, M23 and M26 peptidases, F5/8 type C, vanW or transglycosylase-like. The G5 domain contains a few highly conserved residues. None of these conserved residues are the polar types of amino acids found in active sites, so it seems unlikely this region has an enzymatic function. However, in nearly all cases the G5 domain is associated with a known enzymatic domain. Therefore, the G5 domain may confer localization or substrate specificity on the proteins in which it is found. As a common feature of the proteins containing G5 domains is N-acetylglucosamine binding, it has been suggested that this function might be attributed to the G5 domain. Other alternative functions could be allosteric regulation of the enzymatic domain or cofactor binding [1].

Some proteins known to contain a G5 domain are listed below:

• Staphylococcus aureus plasmin-sensitive surface protein (pls).
• Streptococcal IgA1 peptidases, metallopeptidases that belong to family M26. IgA1 peptidases are important proteins for pathogens that colonise mucosal surfaces. To evade the host immune defences these bacteria produce a peptidase that cleaves IgA1 - the predominant immunoglobulin of mucosal surfaces.
• Streptococcus pneumoniae β-N-acetylhexosaminidase (strH), a glycosyl hydrolase.
• Streptococcus pneumoniae Endo-β-N-acetylglucosaminidase D (Endo D). It cleaves the di-N-acetylchitobiose structure (a 1-4 linked disaccharide of N-acetylglucosamine) in N-linked oligosaccharides and generally acts on complex oligosaccharides after the removal of external sugars by β- galactosidase and β-N-Acetylglucosaminidase.
• Bacterial proteins of the vanW family. The vanW gene is found as part of the Vancomycin resistance gene cluster, but as yet no function has been identified for these proteins.

The profile we developed covers the entire G5 domain.