Bacterial Actin MreB
2016-03-21 12:30 - 13:30 (Europe/London) | United Kingdom
Abstract
Piotr Szwedziak, Thierry Izoré, Fusinita van den Ent, Jan Löwe
The actin-like protein MreB forms filaments that are involved in the maintenance of lateral cell wall in most non-spherical bacteria. The filaments interact with other proteins in the same operon and are directed by periplasmic peptidoglycan remodelling and synthesis machinery.
We have shown that MreB from the T. maritima forms actin-like protofilaments and that probably all MreBs interact directly with the cytoplasmic membrane through an N-terminal amphipathic helix and/or a hydrophobic loop. Removal of the helix has enabled us to obtain biochemistry-grade MreB from C. crescentus. CcMreB forms the same protofilaments as TmMreB and their crystal structures are very similar. The same CcMreB crystals contain an unexpected antiparallel double filament lacking polarity. Using electron microscopy we showed that these double filaments are formed in solution both by CcMreB and TmMreB. We revealed the mode of membrane attachment of MreB by using lipid tubes coated with MreB.
Having the filamentous crystal structure available allowed us to design a non-polymerising mutant of CcMreB and using this mutant we have been able to elucidate the conformational changes leading to polymerisation and ATPase activation upon filament formation. Important mechanistic similarities both to actin and ParM have been uncovered, despite the very different filament architectures. It also enabled the elucidation of the structure of A22 bound to CcMreB, a potent inhibitor.
When liposomes are filled with MreB, they spontaneously change their shape from round to rod-shaped. Upon analysis it is revealed that this is a consequence of MreB filaments forming a helical path around the inside of the liposomes, inducing negative curvature, and this is reminiscent of MreB rings in cells with overexpressed MreB-GFP fusions. We speculate that MreB filaments contain a dedicated hinge that allows the sensing of negative curvature, a property that would allow short filaments, as they exist in normal cells, to sense the short direction of a rod-shaped cell to guide circumferential cell wall growth.
Biography
Jan Löwe’s group focuses on the structure and function of key proteins in the cytoskeleton of bacteria, using all the tools of modern cell and structural biology. Among the molecules he is studying, many of which act as filament-driven motors, are the complex structures involved in bacterial cell division and bacterial chromosome and plasmid segregation. Jan completed his PhD at the Max-Planck Institute in Martinsried with Robert Huber. He then joined the MRC Laboratory of Molecular Biology as an EMBO long-term fellow in 1996, becoming a group leader in 1998. He won a Leverhulme Prize for Biochemistry in 2002, the EMBO Gold Medal in 2007 and has been elected a Fellow of the Royal Society in 2008 and of Germany’s Leopoldina in 2013.
