Biology:Sortase

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Short description: Group of prokaryotic enzymes
Sortase family
Sortase.png
Pilus-related Sortase C of Group B Streptococcus. PDB entry 3O0P[1]
Identifiers
SymbolSortase
PfamPF04203
InterProIPR005754
SCOP21ija / SCOPe / SUPFAM
OPM superfamily294
OPM protein1rz2
CDDcd00004

Sortase refers to a group of prokaryotic enzymes that modify surface proteins by recognizing and cleaving a carboxyl-terminal sorting signal. For most substrates of sortase enzymes, the recognition signal consists of the motif LPXTG (Leu-Pro-any-Thr-Gly), then a highly hydrophobic transmembrane sequence, followed by a cluster of basic residues such as arginine. Cleavage occurs between the Thr and Gly, with transient attachment through the Thr residue to the active site Cys residue, followed by transpeptidation that attaches the protein covalently to cell wall components. Sortases occur in almost all Gram-positive bacteria and the occasional Gram-negative bacterium (e.g. Shewanella putrefaciens) or Archaea (e.g. Methanobacterium thermoautotrophicum), where cell wall LPXTG-mediated decoration has not been reported.[2][3] Although sortase A, the "housekeeping" sortase, typically acts on many protein targets, other forms of sortase recognize variant forms of the cleavage motif, or catalyze the assembly of pilins into pili.[4][5][6]

Reaction

The Staphylococcus aureus sortase is a transpeptidase that attaches surface proteins to the cell wall; it cleaves between the Gly and Thr of the LPXTG motif and catalyses the formation of an amide bond between the carboxyl-group of threonine and the amino-group of the cell-wall peptidoglycan.[7][8]

Biological role

Substrate proteins attached to cell walls by sortases include enzymes, pilins, and adhesion-mediating large surface glycoproteins. These proteins often play important roles in virulence, infection, and colonization by pathogens.

Surface proteins not only promote interaction between the invading pathogen and animal tissues, but also provide ingenious strategies for bacterial escape from the host's immune response. In the case of S. aureus protein A, immunoglobulins are captured on the microbial surface and camouflage bacteria during the invasion of host tissues. S. aureus mutants lacking the srtA gene fail to anchor and display some surface proteins and are impaired in the ability to cause animal infections. Sortase acts on surface proteins that are initiated into the secretion (Sec) pathway and have their signal peptide removed by signal peptidase. The S. aureus genome encodes two sets of sortase and secretion genes. It is conceivable that S. aureus has evolved more than one pathway for the transport of 20 surface proteins to the cell wall envelope.

Note that exosortase and archaeosortase are functionally analogous, while not in any way homologous to sortase.[9]

As an antibiotic target

The sortases are thought to be good targets for new antibiotics[10] as they are important proteins for pathogenic bacteria and some limited commercial interest has been noted by at least one company.[11]

Structure

This group of cysteine peptidases belong to MEROPS peptidase family C60 (clan C-) and include the members of several subfamilies of sortases.

Another sub-family of sortases (C60B in MEROPS) contains bacterial sortase B proteins that are approximately 200 residues long.[12]

Use in structural biology

The transpeptidase activity of sortase is taken advantage of by structural biologists to produce fusion proteins in vitro. The recognition motif (LPXTG) is added to the C-terminus of a protein of interest while an oligo-glycine motif is added to the N-terminus of the second protein to be ligated. Upon addition of sortase to the protein mixture, the two peptides are covalently linked through a native peptide bond. This reaction is employed by NMR spectroscopists to produce NMR invisible solubility tags[13] and by X-ray crystallographers to promote complex formation.[14]

See also

References

  1. ↑ "Structure analysis and site-directed mutagenesis of defined key residues and motives for pilus-related sortase C1 in group B Streptococcus". FASEB Journal 25 (6): 1874–86. June 2011. doi:10.1096/fj.10-174797. PMID 21357525. 
  2. ↑ "Sortase-catalysed anchoring of surface proteins to the cell wall of Staphylococcus aureus". Molecular Microbiology 40 (5): 1049–57. June 2001. doi:10.1046/j.1365-2958.2001.02411.x. PMID 11401711. 
  3. ↑ "Genomic analysis of secretion systems". Current Opinion in Microbiology 6 (5): 519–27. October 2003. doi:10.1016/j.mib.2003.09.005. PMID 14572546. 
  4. ↑ "Sortases make pili from three ingredients". Proceedings of the National Academy of Sciences of the United States of America 105 (37): 13703–4. September 2008. doi:10.1073/pnas.0807334105. PMID 18784365. Bibcode: 2008PNAS..10513703O. 
  5. ↑ "Roles of the sortases of Streptococcus pneumoniae in assembly of the RlrA pilus". Journal of Bacteriology 190 (17): 6002–13. September 2008. doi:10.1128/JB.00379-08. PMID 18606733. 
  6. ↑ Hofmann, Andreas, ed (January 2011). "Crystal structure of Spy0129, a Streptococcus pyogenes class B sortase involved in pilus assembly". PLOS ONE 6 (1): e15969. doi:10.1371/journal.pone.0015969. PMID 21264317. Bibcode: 2011PLoSO...615969K. 
  7. ↑ "Staphylococcus aureus sortase, an enzyme that anchors surface proteins to the cell wall". Science 285 (5428): 760–3. July 1999. doi:10.1126/science.285.5428.760. PMID 10427003. 
  8. ↑ "Sortase, a universal target for therapeutic agents against gram-positive bacteria?". Proceedings of the National Academy of Sciences of the United States of America 97 (10): 5013–5. May 2000. doi:10.1073/pnas.97.10.5013. PMID 10805759. Bibcode: 2000PNAS...97.5013C. 
  9. ↑ "Archaeosortases and exosortases are widely distributed systems linking membrane transit with posttranslational modification". Journal of Bacteriology 194 (1): 36–48. January 2012. doi:10.1128/JB.06026-11. PMID 22037399. 
  10. ↑ "Sortase as a target of anti-infective therapy". Pharmacological Reviews 60 (1): 128–41. March 2008. doi:10.1124/pr.107.07110. PMID 18321961. 
  11. ↑ SIGA Technologies (September 2006). "Schedule 14A". U.S. Securities and Exchange Commission. https://www.sec.gov/Archives/edgar/data/1010086/000095013606007825/file1.htm. 
  12. ↑ "An embarrassment of sortases - a richness of substrates?". Trends in Microbiology 9 (3): 97–102. March 2001. doi:10.1016/S0966-842X(01)01956-4. PMID 11239768. 
  13. ↑ "Attachment of an NMR-invisible solubility enhancement tag using a sortase-mediated protein ligation method". Journal of Biomolecular NMR 43 (3): 145–50. March 2009. doi:10.1007/s10858-008-9296-5. PMID 19140010. 
  14. ↑ "Structural basis for activation and non-canonical catalysis of the Rap GTPase activating protein domain of plexin". eLife 2: e01279. October 2013. doi:10.7554/eLife.01279. PMID 24137545. 

Further reading

This article incorporates text from the public domain Pfam and InterPro: IPR005754



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