THE GATING OF THE BACTERIAL MECHANOSENSITIVE CHANNEL MSCS REFLECTS ITS FUNCTION AS A SENSOR OF BOTH CROWDING AND LATERAL PRESSURE AS WELL AS ITS ROLE IN OSMOREGULATION

Abstract

The mechanosensitive channel MscS is a ubiquitous bacterial membrane valve that opens by increased tension in the event of osmotic down-shock, releasing small internal osmolytes and thus preventing the cell from excessive hydration and possible lysis. This osmolyte release is accompanied by a reduction of osmotic pressure and volume of the cell, which simultaneously increases crowding. The large catalogue of MscS homologs in both prokaryotes and eukaryotes makes the study of this channel enticing to the field of physical biochemistry.

Here are the results of three different studies, two of which focus on the gating of MscS in the presence of large osmolytes and amphipathic compounds and a third which describes the first electrophysiological examination of the inner membrane of the facultative pathogen Vibrio cholerae. The first study in Chapter 2 describes the sensitivity of gating transitions in MscS to large intracellular macromolecules. This sensitivity originates at the cytoplasmic cage domain and the perceived crowding alters the rate of opening, closing and inactivation. Chapter 3 details the utilization of MscS as a sensor for changes in the lateral pressure profile of native bilayers and how this technique can be used to resolve the potential of antibacterial agents to partition into the membrane. The third and final study describes our development of a procedure to generate giant spheroplasts of Vibrio cholerae and the subsequent characterization of its two major mechanosensitive channels in terms of gating, inactivation, conductivity, and compatible osmolyte sensitivity as well as the durability of the pathogen in response to osmotic shock. These contributions to the field of mechanobiology and channel biophysics suggest that environmental feedback during osmoregulation is recognized by the cell, provide a potential method to monitor the partitioning of antibiotics into a cell membrane, and lastly detail the mechano-electrical response of a relevant, disease-causing bacteria.