Domain-based biophysical characterization of the structural and thermal stability of FliG, an essential rotor component of the Na⁺-driven flagellar motor

Abstract

Many bacteria move using their flagellar motor, which generates torque through the interaction between the stator and rotor. The most important component of the rotor for torque generation is FliG. FliG consists of three domains: FliGN, FliGM, and FliGC. FliGC contains a site(s) that interacts with the stator. In this study, we examined the physical properties of three FliG constructs, FliGFull, FliGMC, and FliGC, derived from sodium-driven polar flagella of marine Vibrio. Size exclusion chromatography revealed that FliG changes conformational states under two different pH conditions. Circular dichroism spectroscopy also revealed that the contents of α-helices in FliG slightly changed under these pH conditions. Furthermore, we examined the thermal stability of the FliG constructs using differential scanning calorimetry. Based on the results, we speculate that each domain of FliG denatures independently. This study provides basic information on the biophysical characteristics of FliG, a component of the flagellar motor.

Flagellar Basal Body Structural Proteins FlhB, FliM, and FliY Are Required for Flagellar-Associated Protein Expression in Listeria monocytogenes

“…In addition to FlhB, FliM, and FliY play important roles in the flagellar system of Gram-negative bacteria. FliM is a C-ring component, which plays a role in flagellar assembly and CW/CCW switching of the direction of flagellar rotation ( Onoue et al, 2016 ), in Gram-positive bacteria, its function and mechanism of operation have not been studied and confirmed. FliY is a flagellar rotor protein of the CheC phosphatase family, and it is localized in the flagellar switch complex, which contains the stator-coupling protein FliG and the target of CheY-P, FliM.…”

“…For example, in Escherichia coli CCW rotation allows the several filaments to join in a bundle on a cell and drive it smoothly forward (a ‘run’), while CW rotation destroys the filament bundle and causes rapid somersaulting (a ‘tumble’) ( Blair, 2003 ), while binding of the response regulator phosphorylated CheY (CheY-P) to the rotor switch component FliM and FliN will change the direction of motor swimming ( Delalez et al, 2010 ). FliG, FliM, and FliN belong to the cytoplasmic ring structure, while the MotA/MotB complex is a stator of the flagellar motor that acts as a H + channel to couple the proton flow with torque generation ( Hosking and Manson, 2008 ; Onoue et al, 2016 ). In the process of the bacterial flagella biosynthesis, the greatest challenge is the coordination of the complex flagellar assemble, which requires the timely transcription of the flagellar-associated genes, fine-tuning of intracellular processing, folding and export of flagellar proteins, and the final formation of a functional flagellar filament ( Liu and Ochman, 2007 ).…”