Structural Basis for Type VI Secretion Effector Recognition by a Cognate Immunity Protein

PLoS Pathogens

Eric T. Larson¹  Joseph D. Mougous¹  Isolde Le Trong²  Ronald E. Stenkamp²  Seemay Chou³  Mo Li³  Mike A. Carl³  Justin A. De Leon³  Simon L. Dove⁴ 

[1] Department of Biochemistry, University of Washington, Seattle, Washington, United States of America;Department of Biological Structure, University of Washington, Seattle, Washington, United States of America;Department of Microbiology, University of Washington, Seattle, Washington, United States of America;Division of Infectious Diseases, Children's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America

关键词: Pseudomonas aeruginosa;    Toxins;    Dimers (Chemical physics);    Crystal structure;    Secretion systems;    Immunity;    Secretion;    Cell-mediated immunity;   

DOI  :  10.1371/journal.ppat.1002613

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

The type VI secretion system (T6SS) has emerged as an important mediator of interbacterial interactions. A T6SS from Pseudomonas aeruginosa targets at least three effector proteins, type VI secretion exported 1–3 (Tse1–3), to recipient Gram-negative cells. The Tse2 protein is a cytoplasmic effector that acts as a potent inhibitor of target cell proliferation, thus providing a pronounced fitness advantage for P. aeruginosa donor cells. P. aeruginosa utilizes a dedicated immunity protein, type VI secretion immunity 2 (Tsi2), to protect against endogenous and intercellularly-transferred Tse2. Here we show that Tse2 delivered by the T6SS efficiently induces quiescence, not death, within recipient cells. We demonstrate that despite direct interaction of Tsi2 and Tse2 in the cytoplasm, Tsi2 is dispensable for targeting the toxin to the secretory apparatus. To gain insights into the molecular basis of Tse2 immunity, we solved the 1.00 Å X-ray crystal structure of Tsi2. The structure shows that Tsi2 assembles as a dimer that does not resemble previously characterized immunity or antitoxin proteins. A genetic screen for Tsi2 mutants deficient in Tse2 interaction revealed an acidic patch distal to the Tsi2 homodimer interface that mediates toxin interaction and immunity. Consistent with this finding, we observed that destabilization of the Tsi2 dimer does not impact Tse2 interaction. The molecular insights into Tsi2 structure and function garnered from this study shed light on the mechanisms of T6 effector secretion, and indicate that the Tse2–Tsi2 effector–immunity pair has features distinguishing it from previously characterized toxin–immunity and toxin–antitoxin systems.

【 授权许可】

CC BY