A widespread family of molecular chaperones promotes the intracellular stability of type VIIb secretion system- exported toxins

• 成果类型: Article
• 署名作者: Gkragkopoulou, Polyniki; Garrett, Stephen R.; Shah, Prakhar Y.; Grebenc, Dirk W.; Klein, Timothy A.; Kim, Youngchang; Whitney, John C.
• 署名单位: McMaster University; McMaster University; United States Department of Energy (DOE); Argonne National Laboratory; McMaster University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11431
• DOI: 10.1073/pnas.2503581122
• 发表日期: 2025-09-23
• 关键词: diphtheria-toxin; protein; complex; substrate; reveals; domain; espb

摘要

To survive in highly competitive environments, bacteria use specialized secretion systems to deliver antibacterial toxins into neighboring cells, thereby inhibiting their growth. In many Gram-positive bacteria, the export of such toxins requires a membrane-bound molecular apparatus known as the type VIIb secretion system (T7SSb). Recently, it was shown that toxin recruitment to the T7SSb requires a physical interaction between a toxin and two or more so-called targeting factors, which harbor key residues required for T7SS-dependent protein export. However, in addition to these targeting factors, some toxins additionally require a protein belonging to the DUF4176 protein family. Here, by examining two toxin-DUF4176 protein pairs, we demonstrate that DUF4176 constitutes a family of toxin-specific molecular chaperones. In addition to being required for toxin stability in producing cells, we find that DUF4176 proteins facilitate toxin export by specifically interacting with a previously uncharacterized intrinsically disordered region found in many T7SS toxins. Using X-ray crystallography, we determine structures of several DUF4176 chaperones in their unbound state, and of a DUF4176 chaperone in complex with the binding site of its cognate toxin. These structures reveal that this binding site consists of a disordered amphipathic alpha-helix that requires interaction with its cognate chaperone for proper folding. Overall, we have identified a family of secretion system associated molecular chaperones found throughout T7SSb-containing Gram-positive bacteria.