Infections by Gram-negative pathogens like Salmonella and Shigella rely on type III secretion system (T3SS) effectors. While the opportunistic pathogen Chromobacterium violaceum encodes a crucial T3SS (Cpi-1/-1a), its full effector repertoire remains undefined. Here, we performed a comprehensive proteomic analysis of the C.v. Cpi-1/-1a T3SS secretome. Our analysis not only confirmed known effectors but also unveiled CteX, an effector with no prior functional annotation. Structural determination revealed that CteX adopts a papain-like fold, and functional studies demonstrated that it acts as a cysteine protease that specifically cleaves the focal adhesion adapter protein Paxillinα. This proteolytic activity triggers the collapse of focal adhesions and actin cytoskeleton. CteX-mediated cytoskeletal remodeling limits excessive invasion of epithelial cells by C. violaceum, which could otherwise lead to widespread cell death and premature bacterial exposure. Further, animal infection models confirm that CteX is essential for the virulence and sustained colonization of C. violaceum. Thus, we identify CteX as a T3SS effector that orchestrates bacterial persistence through the unexpected proteolytic targeting of host focal adhesions.
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