Consensus substrate recognition of conserved bacterial virulence peptide-bond recombinase

Shigella OspB, a conserved type 3 effector, is a cysteine protease and peptide recombinase. Developing a protease activity-based screen, we defined and validated an OspB consensus substrate recognition motif. We found that the P1 position is aspartic acid, although cysteine is tolerated, and the P6 position an uncharged nonpolar hydrophobic residue. We demonstrate their predicted proximity to OspB active site residues within a binding groove. These findings will facilitate identification of physiological substrates of OspB and its homologs.