Penicillin-binding proteins in Actinobacteria

Because some Actinobacteria, especially Streptomyces species, are beta-lactam-producing bacteria, they have to have some self-resistant mechanism. The beta-lactam biosynthetic gene clusters include genes for beta-lactamases and penicillin-binding proteins (PBPs), suggesting that these are involved in self-resistance. However, direct evidence for the involvement of beta-lactamases does not exist at the present time. Instead, phylogenetic analysis revealed that PBPs in Streptomyces are distinct in that Streptomyces species have much more PBPs than other Actinobacteria, and that two to three pairs of similar PBPs are present in most Streptomyces species examined. Some of these PBPs bind benzylpenicillin with very low affinity and are highly similar in their amino-acid sequences. Furthermore, other low-affinity PBPs such as SCLAV_4179 in Streptomyces clavuligerus, a beta-lactam-producing Actinobacterium, may strengthen further the self-resistance against beta-lactams. This review discusses the role of PBPs in resistance to benzylpenicillin in Streptomyces belonging to Actinobacteria.