Self-assembly of the bacterial flagellar motor

Fig 1- Cartoon of a flagellum - the FliG ring is part of the aquamarine double-disc structure in the lower membrane

A paper just published in Nature Structural and Molecular Biology, involving Institute staff, and data taken on the Small-Angle X-ray Scattering beamline at the Australian Synchrotron, demonstrates that Escherichia coli FliG, one of the earliest-assembling flagellar motor proteins, forms ordered ring structures via domain-swap polymerization.

Solution structural data, in combination with in vivo biochemical cross-linking experiments and evolutionary covariance analysis, reveals that FliG exists predominantly as a monomer in solution but only as domain-swapped polymers in assembled flagellar motors. A general structural and thermodynamic model for self-assembly is proposed, in which a structural template controls assembly and shapes polymer formation into rings. 

The work is a collaboration involving the Victor Chang Cardiac Research Institute, European Molecular Biology Laboratory Australia, Oxford and Osaka Universities and ANSTO. 

Fig 2- The structure transition studied in the paper

Fig 3- Cartoon illustrating the proposed mechanism of ring formation.

The full reference is M. A. B. Baker, R. M. G. Hynson, L. A. Ganuelas, N. S. Mohammadi, C. W. Liew, A. A. Rey, A. P Duff, A. E Whitten, C. M. Jeffries, N. J. Delalez, Y. V. Morimoto, D. Stock, J. P. Armitage, A. J. Turberfield, K. Namba, R. M. Berry and L. K. Lee, "Domain-swap polymerization drives the self-assembly of the bacterial flagellar motor", Nature Structural and Molecular Biology doi:10.1038/nsmb.3172 (2106).