Long-range coupling regulates stator dynamics in the bacterial flagellar motor

Abstract

The bacterial flagellar motor generates torque through MotAB stator complexes which couple ion flux to rotation. Stators anchor in the peptidoglycan cell wall and dynamically remodel in response to changes in external conditions such as the mechanical load, yet how stator anchoring is regulated remains unknown. Here, we show that long-range allosteric interactions within the MotB periplasmic domain tune stator binding in Escherichia coli. Using coarse-grained elastic-network modeling and co-evolutionary analyses, we identified residues mechanically coupled to peptidoglycan-interacting loops of MotB. Targeted mutagenesis at these coupled sites produced distinct motility phenotypes in some mutants, exhibiting altered swimming speeds compared to wild-type and characteristic expression-dependent swimming trends, indicating mutation-specific effects on stator dynamics or torque. Single-motor measurements distinguished mutants with altered torque from those with altered stator dynamics. Molecular dynamics simulations revealed that mutations at distal positions reshape loop flexibility in ways that quantitatively correlate with swimming speeds. These results demonstrate that allosteric communication within MotB propagates across length scales to modulate the performance of the entire motor, revealing how local molecular changes can tune large-scale bacterial motion.