Enhanced binding of altered H-NS protein to flagellar rotor protein FliG causes increased flagellar rotational speed and hypermotility in Escherichia coli

H-NS is an Escherichia coli nucleoid protein known only to function as a modulator of gene expression. In this study, we found that specific single amino acid substitutions in H-NS caused are approximately 50% increase in flagellum rotational speed. In fluorescence anisotropy and chemical cross-linking assays, H-NS interacted with the flagellar torque-generating rotor protein FliG to form a complex with a K-d of 2.15 mu M. Furthermore, one of the altered H-NS proteins that exhibited high speed flagellum rotation bound FliG 50% tighter than wild-type H-NS. These results demonstrate the first non-regulatory role for H-NS and provide a direct correlation between H-NS-FliG binding affinities, flagellar rotation, and motor torque generation.