Bacterial type IV secretion systems (T4SSs) are a versatile group of nanomachines that can horizontally transfer DNA through conjugation and deliver effector proteins into a wide range of target cells. The components of T4SSs in gram-negative bacteria are organized into several large subassemblies: an inner membrane complex, an outer membrane core complex, and, in some species, an extracellular pilus. Cryo-electron tomography has been used to define the structures of T4SSs in intact bacteria, and high-resolution structural models are now available for isolated core complexes from conjugation systems, the Xanthomonas citri T4SS, the Helicobacter pylori Cag T4SS, and the Legionella pneumophila Dot/Icm T4SS. In this review, we compare the molecular architectures of these T4SSs, focusing especially on the structures of core complexes. We discuss structural features that are shared by multiple T4SSs as well as evolutionary strategies used for T4SS diversification. Finally, we discuss how structural variations among T4SSs may confer specialized functional properties.
Bibliographical noteFunding Information:
This work was supported by NIH AI118932 (TLC, MDO), CA116087 (TLC), AI039657 (TLC), AI164651 (MDO), and the Department of Veterans Affairs (I01BX004447) (TLC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.
- Research Support, N.I.H., Extramural