4 years ago

Structure of the calcium-dependent type 2 secretion pseudopilus.

Nivaskumar, Thomassin, Nilges, Zheng, Egelman, Izadi-Pruneyre, Yu, Bardiaux, Francetic, López-Castilla
Many Gram-negative bacteria use type 2 secretion systems (T2SSs) to secrete proteins involved in virulence and adaptation. Transport of folded proteins via T2SS nanomachines requires the assembly of inner membrane-anchored fibres called pseudopili. Although efficient pseudopilus assembly is essential for protein secretion, structure-based functional analyses are required to unravel the mechanistic link between these processes. Here, we report an atomic model for a T2SS pseudopilus from Klebsiella oxytoca, obtained by fitting the NMR structure of its calcium-bound subunit PulG into the ~5-Å-resolution cryo-electron microscopy reconstruction of assembled fibres. This structure reveals the comprehensive network of inter-subunit contacts and unexpected features, including a disordered central region of the PulG helical stem, and highly flexible C-terminal residues on the fibre surface. NMR, mutagenesis and functional analyses highlight the key role of calcium in PulG folding and stability. Fibre disassembly in the absence of calcium provides a basis for pseudopilus length control, essential for protein secretion, and supports the Archimedes screw model for the type 2 secretion mechanism.An atomic model for a type 2 secretion system pseudopilus from Klebsiella oxytoca reveals a comprehensive network of inter-subunit contacts while mutational and functional analyses highlight the role of calcium in PulG folding and stability.

Publisher URL: http://doi.org/10.1038/s41564-017-0041-2

DOI: 10.1038/s41564-017-0041-2

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