Bacteriophage Twort protein Gp168 is a β-clamp inhibitor by occupying the DNA sliding channel.

Abstract

Bacterial chromosome replication is mainly catalyzed by DNA polymerase III, whose beta subunits enable rapid processive DNA replication. Enabled by the clamp-loading complex, the two beta subunits form a ring-like clamp around DNA and keep the polymerase sliding along. Given the essential role of β-clamp, its inhibitors have been explored for antibacterial purposes. Similarly, β-clamp is an ideal target for bacteriophages to shut off host DNA synthesis during host takeover. The Gp168 protein of phage Twort is such an example, which binds to the β-clamp of Staphylococcus aureus and prevents it from loading onto DNA causing replication arrest. Here, we report a cryo-EM structure of the clamp–Gp168 complex at 3.2-Å resolution. In the structure of the complex, the Gp168 dimer occupies the DNA sliding channel of β-clamp and blocks its loading onto DNA, which represents a new inhibitory mechanism against β-clamp function. Interestingly, the key residues responsible for this interaction on the β-clamp are well conserved among bacteria. We therefore demonstrate that Gp168 is potentially a cross-species β-clamp inhibitor, as it forms complex with the Bacillus subtilis β-clamp. Our findings reveal an alternative mechanism for bacteriophages to inhibit β-clamp and provide a new strategy to combat bacterial drug resistance.