ClpAClpC

ClpA and ClpC are ATP-dependent chaperones that regulate proteolysis in bacteria by partnering with the ClpP proteolytic core. They are part of the AAA+ (ATPases Associated with diverse cellular Activities) family and function as unfoldases that recognize, unfold, and translocate substrates into ClpP for degradation. While often discussed together, ClpA and ClpC are distinct proteins that form separate protease machines with ClpP.

ClpP forms a barrel-shaped tetradecamer that provides the proteolytic chamber. ClpA associates directly with ClpP to form the ClpAP protease, delivering substrates for degradation without requiring additional adapters in many species. ClpC, by contrast, typically relies on adaptor proteins in certain bacteria (for example MecA in Bacillus subtilis) to recognize specific substrates and present them to the ClpC-ClpP protease. These adaptors help regulate substrate specificity and the timing of degradation.

Structurally, ClpA and ClpC are hexameric AAA+ ATPases with two active ATPase domains per subunit and an N-terminal or coiled-coil domain that mediates substrate or adaptor interactions. ATP binding and hydrolysis drive conformational changes that unfold target proteins and translocate them into ClpP for proteolysis. The system is highly regulated and central to proteostasis, stress responses, and the turnover of regulatory proteins in bacteria.

Distribution and function: ClpAP and ClpCP proteases are widely distributed across bacteria. ClpAP is common in Gram-negative species, whereas ClpCP is more characteristic of certain Gram-positive bacteria with MecA- or similar-adaptor systems. Together, ClpA and ClpC contribute to removing misfolded proteins, regulating cellular processes, and enabling adaptation to environmental stresses.

Clinical relevance: The ClpP protease is a known antibiotic target, and disrupting ClpA- or ClpC-mediated proteolysis can affect bacterial virulence and stress tolerance. Inhibitors targeting the ATPase components or adaptor interactions are an area of ongoing research.