Correlating a protein structure with function of a bacterial mechanosensitive channel

MscL, a mechanosensitive channel found in many bacteria, protects cells fro m hypotonic shock by reducing intracellular pressure through release of cyt oplasmic osmolytes. First isolated from Escherichia coli, this protein has served as a model for how a protein senses and responds to membrane tension . Recently the structure of a functionally uncharacterized MscL homologue f rom Mycobacterium tuberculosis was solved by x-ray diffraction to a resolut ion of 3.5 Angstrom Here we demonstrate that the protein forms a functional MscL-like mechanosensitive channel in E, coli membranes and azolectin prot eoliposomes Furthermore, we show that M. tuberculosis MscL crystals, when r e-solubilized and reconstituted, yield wild-type channel currents in patch damp, demonstrating that the protein does not irreversibly change conformat ion upon crystallization. Finally, we apply functional clues acquired from the E, coli MscL to the M. tuberculosis channel and show a mechanistic corr elation between these channels. However, the inability of the M. tuberculos is channel to gate at physiological membrane tensions, demonstrated by in v ivo E. coli expression and in vitro reconstitution, suggests that the membr ane environment or other additional factors influence the gating of this ch annel.