Exosortase refers to a family of integral membrane proteins that occur in Gram-negative bacteria that recognizes and cleaves the carboxyl-terminal sorting signal PEP-CTERM.
[1][2] The name derives from a predicted role analogous to sortase, despite the lack of any detectable sequence homology, and a strong association of exosortase genes with exopolysaccharide or extracellular polymeric substance biosynthesis loci.
Archaeosortase A recognizes the signal PGF-CTERM, found at the C-terminus of some archaeal S-layer proteins.
However, site-directed mutagenesis work on archaeosortase A, an archaeal homolog of exosortases, strongly supports the notion of a Cys active site and convergent evolution with sortase family transpeptidases.
[3] A recent study on Zoogloea resiniphila, a bacterium found in activated sludge wastewater treatment plants, has shown that PEP-CTERM proteins (and by implication, exosortase as well) are essential to floc formation in some systems.