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Bacterial actin MreB forms antiparallel double filaments
Fusinita van den Ent1, Thierry Izoré2, Tanmay Am Bharat2
1Structural Studies Division, Medical Research Council - Laboratory of Molecular Biology, Cambridge, United Kingdom fent@mrc-lmb.cam.ac.uk.
Abstract:
Filaments of all actin-like proteins known to date are assembled from pairs of protofilaments that are arranged in a parallel fashion, generating polarity. In this study, we show that the prokaryotic actin homologue MreB forms pairs of protofilaments that adopt an antiparallel arrangement in vitro and in vivo. We provide an atomic view of antiparallel protofilaments of Caulobacter MreB as apparent from crystal structures. We show that a protofilament doublet is essential for MreB's function in cell shape maintenance and demonstrate by in vivo site-specific cross-linking the antiparallel orientation of MreB protofilaments in E. coli. 3D cryo-EM shows that pairs of protofilaments of Caulobacter MreB tightly bind to membranes. Crystal structures of different nucleotide and polymerisation states of Caulobacter MreB reveal conserved conformational changes accompanying antiparallel filament formation. Finally, the antimicrobial agents A22/MP265 are shown to bind close to the bound nucleotide of MreB, presumably preventing nucleotide hydrolysis and destabilising double protofilaments.DOI: http://dx.doi.org/10.7554/eLife.02634.001.
Insights
Prokaryotic actin MreB forms antiparallel protofilament pairs, unlike other actin-like proteins. This unique structure is crucial for bacterial cell shape maintenance and is targeted by antimicrobial agents.
Area of Science:
- Cellular Biology
- Microbiology
- Biochemistry
Background:
- Actin-like proteins typically form parallel protofilaments, establishing cellular polarity.
- The bacterial actin homologue MreB is essential for maintaining bacterial cell shape.
Purpose of the Study:
- To investigate the in vitro and in vivo assembly of MreB protofilaments.
- To elucidate the structural basis of MreB's role in cell shape maintenance.
- To understand the mechanism of action of MreB-targeting antimicrobial agents.
Main Methods:
- X-ray crystallography to determine atomic structures of MreB protofilaments.
- 3D cryo-electron microscopy (cryo-EM) to visualize MreB-membrane interactions.
- In vivo site-specific cross-linking to confirm protofilament orientation in E. coli.
Main Results:
- MreB forms antiparallel protofilament pairs in vitro and in vivo, a novel arrangement for actin-like proteins.
- Antiparallel protofilament doublets are essential for MreB's function in cell shape maintenance.
- Crystal structures reveal conformational changes associated with antiparallel filament formation.
- Antimicrobial agents A22/MP265 bind to MreB near the nucleotide, inhibiting hydrolysis and destabilizing protofilament doublets.
Conclusions:
- Bacterial actin MreB exhibits an atypical antiparallel protofilament assembly.
- This unique structure is critical for bacterial morphogenesis and represents a target for novel antimicrobials.