Bridging the N-terminal and middle domains in FliG of the flagellar rotor

Dagnija Tupiņa; Alexander Krah; Jan K Marzinek; Lorena Zuzic; Adam A Moverley; Chrystala Constantinidou; Peter J Bond

doi:10.1016/j.crstbi.2022.02.002

Bridging the N-terminal and middle domains in FliG of the flagellar rotor

Curr Res Struct Biol. 2022 Mar 12:4:59-67. doi: 10.1016/j.crstbi.2022.02.002. eCollection 2022.

Authors

Dagnija Tupiņa^{1

2}, Alexander Krah¹, Jan K Marzinek¹, Lorena Zuzic^{1

3}, Adam A Moverley⁴, Chrystala Constantinidou², Peter J Bond^{1

5}

Affiliations

¹ Bioinformatics Institute, A∗STAR, 30 Biopolis Street, 138671, Singapore.
² Warwick Medical School, University of Warwick, Coventry, CV4 7AL, United Kingdom.
³ Department of Chemistry, Faculty of Science and Engineering, Manchester Institute of Biotechnology, The University of Manchester, Manchester, M1 7DN, United Kingdom.
⁴ Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, United Kingdom.
⁵ Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543, Singapore.

Abstract

Flagella are necessary for bacterial movement and contribute to various aspects of virulence. They are complex cylindrical structures built of multiple molecular rings with self-assembly properties. The flagellar rotor is composed of the MS-ring and the C-ring. The FliG protein of the C-ring is central to flagellar assembly and function due to its roles in linking the C-ring with the MS-ring and in torque transmission from stator to rotor. No high-resolution structure of an assembled C-ring has been resolved to date, and the conformation adopted by FliG within the ring is unclear due to variations in available crystallographic data. Here, we use molecular dynamics (MD) simulations to study the conformation and dynamics of FliG in different states of assembly, including both in physiologically relevant and crystallographic lattice environments. We conclude that the linker between the FliG N-terminal and middle domain likely adopts an extended helical conformation in vivo, in contrast with the contracted conformation observed in some previous X-ray studies. We further support our findings with integrative model building of full-length FliG and a FliG ring model that is compatible with cryo-electron tomography (cryo-ET) and electron microscopy (EM) densities of the C-ring. Collectively, our study contributes to a better mechanistic understanding of the flagellar rotor assembly and its function.

Keywords: CCW, counter-clockwise; CW, clock-wise; MD, Molecular Dynamics; MDFF, Molecular Dynamics Flexible Fitting; cryo-ET, cryo-electron tomography.