Elżbieta Jagielska attended The Lysing Meeting (3-8 Nov 2018) in New York, USA and presented recent results on peptidoglycan recognition and binding by lysostaphin.
Peptidoglycan recognition by lysostaphin SH3b domain
Lysostaphin is the most studied potential antimicrobial agent, which belongs to class III bacteriocins. The enzyme is a peptidoglycan hydrolase derived from Staphylococcus simulans that cleaves pentaglycine bridges in the staphylococcal cell wall peptidoglycans, characteristic for e.g. Staphylococcus aureus. The specificity for the pentaglycine cross-bridge is very high, therefore staphylococcal strains which develop substitutions in the bridge region by introducing serine residue instead of glycine, are no longer susceptible to lysostaphin. Mature lysostaphin is a two-domain enzyme, consisting of an N-terminal catalytic domain (Lss_CD) and a C-terminal cell wall binding domain (Lss_SH3b). SH3b domains are necessary for accurate cell wall recognition and regulation of catalytic activity of peptidoglycan hydrolases. Structures of SH3b domains have so far been determined for Ale-1 and lysostaphin, both in the absence of their ligands. We are presenting the first bacterial SH3b domain in complex with pentaglycine, which does not entail significant allosteric changes. High resolution structure (PDB ID: 5LEO) reveals details of pentaglycine binding mode: 1) identifies binding grove between β1 and β2 strands, 2) indicates pentaglycine specificity which is a combination of direct (steric exclusion) and indirect (substrate main chain conformations’ selection accessible only for pentaglycine) effects, 3) and allows for further bioinformatic analysis of stem peptides interactions with SH3b domain. Based on the structural data we have engineered lysostaphin SH3b domain and tested the relevance of the introduced changes in binding affinity and the bacteriolytic activity of mature lysostaphin. Presented results are relevant not only for understanding lysostaphin specificity but may also laid the bases for addressing the problem of lysostaphin resistance.