Archaeosortase

An archaeosortase is a protein that occurs in the cell membranes of some archaea.[1] Archaeosortases recognize and remove carboxyl-terminal protein sorting signals about 25 amino acids long from secreted proteins. A genome that encodes one archaeosortase may encode over fifty target proteins. The best characterized archaeosortase target is the Haloferax volcanii S-layer glycoprotein, an extensively modified protein with O-linked glycosylations, N-linked glycosylations, and a large prenyl-derived lipid modification toward the C-terminus.[2] Knockout of the archaeosortase A (artA) gene, or permutation of the motif Pro-Gly-Phe (PGF) to Pro-Phe-Gly in the S-layer glycoprotein, blocks attachment of the lipid moiety as well as blocking removal of the PGF-CTERM protein-sorting domain.[3] Thus archaeosortase appears to be a transpeptidase, like sortase, rather than a simple protease.

Archaeosortases are related to exosortases, their uncharacterized counterparts in Gram-negative bacteria. The names of both families of proteins reflect roles analogous to sortases in Gram-positive bacteria, with which they share no sequence homology. The sequences of archaeosortases and exosortases consists mostly of hydrophobic transmembrane helices, which sortases lack. Archaeosortases fall into a number of distinct subtypes, each responsible for recognizing sorting signals with a different signature motif. Archaeosortase A (ArtA) recognizes the PGF-CTERM signal, ArtB recognizes VPXXXP-CTERM, AtrC recognizes PEF-CTERM, and so on; one archaeal genome may encode two different archaeosortase systems.

Invariant residues shared by all archaeosortases and exosortases include a Cys and an Arg. Replacement of either destroys catalytic activity, suggesting convergent evolution of the active site with the sortases.[4]

In the archaeal model species Haloferax volcanii, archaeosortase A belongs to a fairly large collection of identified membrane-associated proteases, but apparently also to the smaller set of intramembrane cleaving proteases, along with the rhomboid protease RhoII, and in contrast to bacterial sortases.[5]

References
  1. Haft, Daniel H.; Samuel H. Payne; Jeremy D. Selengut (January 2012). "Archaeosortases and Exosortases Are Widely Distributed Systems Linking Membrane Transit with Posttranslational Modification". J. Bacteriol. 194 (1): 36–48. doi:10.1128/JB.06026-11. PMC 3256604. PMID 22037399.
  2. "Haloferax volcanii archaeosortase is required for motility, mating, and C-terminal processing of the S-layer glycoprotein". Mol Microbiol. 88 (6): 1164–75. Jun 2013. doi:10.1111/mmi.12248. PMID 23651326.
  3. Abdul Halim, MF; Karch, KR; Zhou, Y; Haft, DH; Garcia, BA; Pohlschroder, M (2016). "Permuting the PGF Signature Motif Blocks both Archaeosortase-Dependent C-Terminal Cleavage and Prenyl Lipid Attachment for the Haloferax volcanii S-Layer Glycoprotein". J. Bacteriol. 198: 808–15. doi:10.1128/JB.00849-15. PMC 4810604. PMID 26712937.
  4. 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.
  5. Giménez MI, Cerletti M, De Castro RE (2015). "Archaeal membrane-associated proteases: insights on Haloferax volcanii and other haloarchaea". Frontiers in Microbiology. 6: 39. doi:10.3389/fmicb.2015.00039. PMC 4343526. PMID 25774151.
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