Exosortase

Exosortase refers to a family of integral membrane proteins that occur in Gram-negative bacteria and that recognize and cleave 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. Many archaea have an archaeosortase, homologous to exosortases rather than to sortases. Archaeosortase A recognizes the signal PGF-CTERM, found at the C-terminus of some archaeal S-layer proteins. Following processing by archaeosortase A, the PGF-CTERM region is gone, and a prenyl-derived lipid anchor is present at the C-terminus instead.

Transmembrane exosortase (Exosortase_EpsH)
Identifiers
SymbolExosortase_EpsH
PfamPF09721

Exosortase has not itself been characterized biochemically. 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 [4].

References
  1. Haft DH, Paulsen IT, Ward N, Selengut JD (August 2006). "Exopolysaccharide-associated protein sorting in environmental organisms: the PEP-CTERM/EpsH system. Application of a novel phylogenetic profiling heuristic". BMC Biology. 4: 29. doi:10.1186/1741-7007-4-29. PMC 1569441. PMID 16930487.
  2. Haft DH, Payne SH, Selengut JD (January 2012). "Archaeosortases and exosortases are widely distributed systems linking membrane transit with posttranslational modification". Journal of Bacteriology. 194 (1): 36–48. doi:10.1128/JB.06026-11. PMC 3256604. PMID 22037399.
  3. Abdul Halim MF, Rodriguez R, Stoltzfus JD, Duggin IG, Pohlschroder M (May 2018). "Conserved residues are critical for Haloferax volcanii archaeosortase catalytic activity: Implications for convergent evolution of the catalytic mechanisms of non-homologous sortases from archaea and bacteria". Molecular Microbiology. 108 (3): 276–287. doi:10.1111/mmi.13935. PMID 29465796.
  4. Gao N, Xia M, Dai J, Yu D, An W, Li S, Liu S, He P, Zhang L, Wu Z, Bi X, Chen S, Haft DH, Qiu D (May 2018). "Both widespread PEP-CTERM proteins and exopolysaccharides are required for floc formation of Zoogloea resiniphila and other activated sludge bacteria". Environmental Microbiology. 20 (5): 1677–1692. doi:10.1111/1462-2920.14080. PMID 29473278.


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