Solving the Type VI secretion puzzle: understanding subcomplexes organization and dynamics by a multidisciplinary approach – FullContact

The type VI secretion system is a contractile nanomachine evolved by bacteria to destroy their rivals. It is composed of fourteen subunits that assemble into three sub-complexes: the membrane complex (MC), the baseplate (BP) and the tail tube/sheath complex (TTC). The high-resolution structures of these complexes are known, except the BP for which only the repetitive wedge complex that polymerizes around the hub has been recently determined. In this project, we will combine the expertise of our two teams to define the structure of the fully assembled BP, and to identify the contacts that BP subunits establish with the MC and the TTC. We will use a combination of cryo-electron microscopy, cryo-electron tomography and in vivo cross-linking after orthogonal labeling with non-natural photoreactive amino-acids. These data will provide an unprecedented view on how the different sub-complexes interact with each other and a globale picture of the assembled secretion system. By defining the BP-MC contacts, we expect to structurally understand the symmetry mismatch between these two sub-complexes. These studies will be performed in wild-type cells but also using genetic artifices allowing to hold the secretion apparatus at distinct stages of its biogenesis and mechanism of action, to obtain a dynamic understanding of the contacts that are established during T6SS assembly and after contraction.