Symmetry-Constrained Normal Mode Analysis of the Bacterial Flagellar Motor

Abstract

AbstractThe bacterial flagellar motor is a locomotive organelle which helps cell propel in liquid environment. The cytoplasmic ring called C-ring, composed of three proteins such as FliG, FliM, and FliN, is mostly involved in rotational motion of this biological motor system. C-ring interacts with stator proteins (Mot A/B) to regulate both clockwise and counter-clockwise rotations (1). Some stoichiometry study of switch complex components indicates that structure of C-ring is unstable and changeable upon rotational direction (2). Furthermore, FliG structure changes depending on the connection state of Helixmc between adjacent FliGs (3). It also remains unclear how switch mechanism occurs in C-ring and what mainly affects this bidirectional rotation.In this study, we reconstruct a C-ring structure by using three known protein structures (3HJL,3AJC,4FHR) in order to investigate its switching mechanism although the C-ring structure rapidly changes in switching motion. Then, we apply a symmetry-constrained elastic network model (SCENM) to the C-ring structure in order to model efficiently both intra and inter-connectivity among its repeated subunits (4).Normal mode analysis for this SCENM not only reveals several intrinsic collective motions of the C-ring structure, but also indicates, more importantly, that orientation of Helixmc plays a crucial role in switching mechanism of the bacterial flagellar motor by directly affecting the conformational change in FliG domain.References(1) Zhou, J. et al. 1998. Proc. Natl. Acad. Sci. U. S. A. 95:6436-6441.(2) Delalez, N. J. et al. 2014. MBio 5: e01216-e01214.(3) Minamino, T. et al. 2011. PLoS Biol. 9: e1000616(4) Kim, M. K. et al. 2003. J. Struct. Biol. 143:107-117