Exosortase Explained

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. 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.

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]

Notes and References

1. Haft DH, Paulsen IT, Ward N, Selengut JD . Exopolysaccharide-associated protein sorting in environmental organisms: the PEP-CTERM/EpsH system. Application of a novel phylogenetic profiling heuristic . BMC Biology . 4 . 29 . August 2006 . 16930487 . 1569441 . 10.1186/1741-7007-4-29 . free .
2. Haft DH, Payne SH, Selengut JD . Archaeosortases and exosortases are widely distributed systems linking membrane transit with posttranslational modification . Journal of Bacteriology . 194 . 1 . 36–48 . January 2012 . 22037399 . 3256604 . 10.1128/JB.06026-11 .
3. Abdul Halim MF, Rodriguez R, Stoltzfus JD, Duggin IG, Pohlschroder M . 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 . May 2018 . 29465796 . 10.1111/mmi.13935 . free .
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 . 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 . May 2018 . 29473278 . 10.1111/1462-2920.14080 . 4341022 . 2019-12-14 . 2021-01-21 . https://web.archive.org/web/20210121055907/http://ir.ihb.ac.cn/handle/342005/29334 . dead .