Protein-sorting transpeptidase

A protein-sorting transpeptidase is an enzyme, such as the sortase SrtA[1] of Staphylococcus aureus, that cleaves one or more target proteins produced by the same cell, as part of a specialized pathway of protein targeting. The typical prokaryotic protein-sorting transpeptidase is characterized as a protease, but does not simply hydrolyze a peptide bond. Instead, the larger, N-terminal portion of the cleaved polypeptide is transferred onto another molecule, such as a precursor of the peptidoglycan cell wall in Gram-positive bacteria.

The term sortase is properly reserved for the set of cysteine protease enzymes sortase A, sortase B, and members of additional classes, all of which share homology. However, a growing number of additional protein sorting systems has been described in prokaryotes, involving sorting enzymes that lack any homology to sortase and that appear to have arisen separately by convergent evolution. Although the sortases are the best described members of the protein-sorting transpeptidases, work on the analogous enzymes archaeosortase[2], rhombosortase[3], and the PorU enzyme of type IX secretion systems (T9SS)[4] has been accumulating.

sorting enzyme mechanism cognate sorting signal
sortase A cysteine protease LPXTG
sortase B cysteine protease NPQTN
archaeosortase A cysteine protease PGF-CTERM
exosortase A cysteine protease PEP-CTERM
rhombosortase serine protease GlyGly-CTERM
PorU as in Porphyromonas gingivalis serine protease T9SS C-terminal beta-sandwich domain

References
  1. Zong Y, Bice TW, Ton-That H, Schneewind O, Narayana SV (2004). "Crystal structures of Staphylococcus aureus sortase A and its substrate complex". J Biol Chem. 279 (30): 31383–9. doi:10.1074/jbc.M401374200. PMID 15117963.
  2. Abdul Halim MF, Rodriguez R, Stoltzfus JD, Duggin IG, Pohlschroder M (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". Mol Microbiol. 108 (3): 276–287. doi:10.1111/mmi.13935. PMID 29465796.
  3. Gadwal S, Johnson TL, Remmer H, Sandkvist M (2018). "C-terminal processing of GlyGly-CTERM containing proteins by rhombosortase in Vibrio cholerae". PLoS Pathog. 14 (10): e1007341. doi:10.1371/journal.ppat.1007341. PMC 6219818. PMID 30352106.
  4. de Diego I, Ksiazek M, Mizgalska D, Koneru L, Golik P, Szmigielski B, et al. (2016). "The outer-membrane export signal of Porphyromonas gingivalis type IX secretion system (T9SS) is a conserved C-terminal β-sandwich domain". Sci Rep. 6: 23123. doi:10.1038/srep23123. PMC 4804311. PMID 27005013.
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