Physiology and structure of pathogenic Escherichia coli pOmpT reveal two substrate-binding sites

The pathogenicity of bacteria can be achieved by cleaving antimicrobial peptides (AMPs) through the outer membrane protease family (Omptins) to evade or resist the host’s innate immune response. The OmpT-like proteins in Escherichia coli are members of Omptins, which have highly conserved proteolytic activity. Here, sequence alignment and physiological studies have determined that pOmpT is a virulence factor with atypical proteolytic activity. Comparing pOmpT with cOmpT in terms of structure, proteolytic activity and target substrates, it is found that Asp 267 and Ser 276 of cOmpT are substrate-binding sites and help its catalytic center to cleave substrates (protamine,synthetic peptide or RNase 7). However, special structural features and the nature of residues Ser 267 and Thr 276 of pOmpT caused the inability of cleavage protamine, but allows it to specifically cleave the human AMP RNase 7. It is suggested that two sites are related with the substrate specificity. In short, we found that pOmpT presents a new structural basis for the specific recognition of substrates, and providing new clues for the development of antimicrobial drugs.