Coevolution-Guided Mapping of the Type VI Secretion Membrane Complex-Baseplate Interface

The type VI secretion system (T6SS) is a multiprotein weapon evolved by Gram-negative bacteria to deli-ver effectors into eukaryotic cells or bacterial rivals. The T6SS uses a contractile mechanism to propel an effector-loaded needle into its target. The contractile tail is built on an assembly platform, the baseplate, which is anchored to a membrane complex. Baseplate-membrane complex interactions are mainly medi-ated by contacts between the C-terminal domain of the TssK baseplate component and the cytoplasmic domain of the TssL inner membrane protein. Currently, the structural details of this interaction are unknown due to the marginal stability of the TssK-TssL complex. Here we conducted a mutagenesis study based on putative TssK-TssL contact pairs identified by co-evolution analyses. We then evaluated the impact of these mutations on T6SS activity, TssK-TssL interaction and sheath assembly and dynamics in enteroaggregative Escherichia coli. Finally, we probed the TssK-TssL interface by disulfide cross -linking, allowing to propose a model for the baseplate-membrane complex interface.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The T6SS is a multiprotein weapon evolved by Gram-negative bacteria to deliver effectors into cells. The interactions between the TssK baseplate component and the TssL inner membrane protein are important for T6SS activity. In this study, mutagenesis and cross-linking analyses were used to investigate the structural details and propose a model for the baseplate-membrane complex interface.