Assembly of Bacillus subtilis Dynamin into Membrane-Protective Structures in Response to Environmental Stress Is Mediated by Moderate Changes in Dynamics at a Single Molecule Level.

Dynamin-like proteins are membrane-associated GTPases, conserved in bacteria and in eukaryotes, that can mediate nucleotide-driven membrane deformation or membrane fusion reactions. Bacillus subtilis' DynA has been shown to play an important role in protecting cells against chemicals that induce membrane leakage, and to form an increased number of membrane-associated structures after induction of membrane stress. We have studied the dynamics of DynA at a single molecule level in real time, to investigate how assembly of stress-induced structures is accompanied by changes in molecule dynamics. We show that DynA molecule displacements are best described by the existence of three distinct populations, a static mode, a low-mobility, and a fast-mobile state. Thus, DynA is most likely freely diffusive within the cytosol, moves along the cell membrane with a low mobility, and arrests at division sites or at stress-induced lesions at the membrane. In response to stress-inducing membrane leakage, but not to general stress, DynA molecules become slightly more static, but largely retain their mobility, suggesting that only few molecules are involved in the repair of membrane lesions, while most molecules remain in a dynamic mode scanning for lesions. Our data suggest that even moderate changes in single molecule dynamics can lead to visible changes in protein localization patterns.