Penicillin-binding proteins (PBPs) are biosynthetic enzymes involved in bacterial cell wall assembly. Structurally they are evolutionarily related to β-lactamases, the class of enzymes that mediate resistance to β-lactam antibiotics (Meroueh, 2003). Thus, (PBPs) are often seen as a possible mediator of resistance in bacteria when challenged with β-lactam antibiotics.
Within normal bacterial growth and development, PBPs are a family of enzymes responsible for the polymerization of the glycan strand and the cross-linking between glycan chains. Mutational alterations in PBPs can confer resistance either by reducing binding of the antibiotic to the active site or by evolving a β-lactamase activity that degrades the antibiotic.
PBPs can be classified into two groups: low molecular weight PBPs and high molecular weight PBPs, each of which have been subdivided into three classes based on amino-acid sequence similarities (Ghuysen 1991).
PBPs in the genomes of Orientia isolates:
Three loci have been identified in the genomes of 14 isolates from O. tsutsugamushi and from the genome of O. chuto. All isolates were found to have each of the three loci. Two of these show homology with loci classified as penicillin-binding protein 2, while one is classified as penicillin-binding protein 4. The loci, together with the location of the locus within the genome of the Boryong isolate are:
penicillin-binding protein 4 – Boryong: 190158..191369; homologous with locus pbpE in Rickettsia bellii.
penicillin-binding protein 2 – Boryong: 674301..676052; homologous with locus pbpA2 in Rickettsia bellii.
penicillin-binding protein 2 – Boryong: 2118743..2120491; homologous with locus pbpA1 in Rickettsia bellii.