Small molecules activate Staphylococcus aureus ClpC protease

Researchers have been pursuing new ways to hit bacterial weaknesses without relying on traditional antibiotics. One promising target is the central AAA+ ClpC/ClpP protease found in Gram-positive bacteria; it helps pathogens survive stress and is important for virulence, so it has been recognized as a drug target. Natural cyclic peptides that deregulate the essential Mycobacterium tuberculosis ClpC1 already show that messing with these proteases can kill bacteria, and genetic studies have shown that overactivated mutants of the non-essential Staphylococcus aureus ClpC homologue trigger uncontrolled proteolysis and severe toxicity in vivo. Despite this background, no chemical modulators of S. aureus ClpC had been reported. To address that gap, a team led by corresponding author Axel Mogk set out to search for small molecules that change how ClpC works. Using a biochemical high-throughput screen, they hunted for compounds that alter ClpC activity and followed up with detailed analyses to understand how any hits work. The goal was to determine whether ClpC can be chemically targeted and, if so, where small molecules might bind and alter its regulation.

The researchers applied a biochemical high-throughput screen and identified eight chemically distinct bona fide small molecules that robustly stimulate ClpC ATPase and proteolytic activity in vitro. These hits were then probed using structural, computational, and mutational analyses to find where and how the compounds act on the enzyme. Those follow-up experiments converged on two ligandable regulatory sites within the ClpC N-terminal domain (NTD) as compound targets: a conserved hydrophobic groove and an allosteric pArg1 pocket. Both of these sites are known to be engaged in substrate recognition, linking compound binding to the enzyme’s normal control mechanisms. By combining activity assays with structural and computational mapping and targeted mutations, the study established that small molecules can directly engage regulatory features of S. aureus ClpC and dial up its ATPase and proteolytic functions in vitro.

The work has two immediate implications. First, it establishes S. aureus ClpC as chemically targetable: small molecules can bind defined pockets in the ClpC N-terminal domain and alter its activity, showing that protease regulation in this system can be hijacked by designed compounds. Second, the identification of a conserved hydrophobic groove and an allosteric pArg1 pocket gives a clear mechanistic picture of the regulatory architecture researchers can exploit. Because overactivation of ClpC can cause uncontrolled proteolysis and toxicity in bacteria, chemical reagents that mimic those effects could become starting points for antimicrobials that break bacterial stress responses and virulence. At the same time, optimized chemical probes emerging from this work will help scientists study AAA+ protease control in detail. The authors highlight that these findings enable future development and optimization of chemical probes to deregulate AAA+ protease control, a step toward both basic understanding and potential therapeutic strategies.