Baseplate component TssK and spatio-temporal assembly of T6SS in $Pseudomonas\ aeruginosa$
Résumé
The Gram-negative bacteria use the contractile multi-molecular structure, called the
Type VI Secretion System (T6SS) to inject toxic products into eukaryotic and prokaryotic
cells. In this study, we use fluorescent protein fusions and time-lapse microscopy
imaging to study the assembly dynamics of the baseplate protein TssK in Pseudomonas
aeruginosa T6SS. TssK formed transient higher-order structures that correlated with
dynamics of sheath component TssB. Assembly of peri-membrane TssK structures
occurred de novo upon contact with competing bacteria. We show that this assembly
required presence of TagQ-TagR envelope sensors, activity of PpkA kinase and
anchoring to the inner membrane via TssM. Disassembly and repositioning of TssK
component was dependent on PppA phosphatase and indispensable for repositioning
and deployment of the entire contractile apparatus toward a new target cell. We
also show that TssE is necessary for correct elongation and stability of TssB-sheath,
but not for TssK assembly. Therefore, in P. aeruginosa, assembly of the TssKcontaining structure relays on the post-translational regulatory envelope module and
acts as spatio-temporal marker for further recruitment and subsequent assembly of the
contractile apparatus
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