The Role of the C-Terminal Domain on the Gating Properties of Corynebacterium Glutamicum Mechanosensitive Channel MscCG

The gram-positive soil bacterium Corynebacterium glutamicum exports a large amount of glutamate through the mechanosensitive channel MscCG. This process is utilized for the world industrial glutamate production. MscCG belongs to a subfamily of bacterial MscS-like channels, which function in osmoregulation, however this channel shows structural and functional differences compared to MscS. To understand the role of the carboxyl terminal domain of MscCG, the chimeric channel MscS-(C-MscCG), which is a fusion protein between the carboxyl terminal domain of MscCG and the MscS channel, was examined by the patch clamp technique. We found that the chimeric channel exhibited MS channel activity in E. coli spheroplasts characterized by a lower activation threshold and slow channel closing compared to MscS. The chimeric channel MscS-(C-MscCG) was also successfully reconstituted into azolectin liposomes and exhibited gating hysteresis in a voltage-dependent manner, especially at high pipette voltages. Moreover, the channel remained open after releasing pipette pressure at membrane potentials physiologically relevant for the Corynebacterium glutamicum cells. This contribution to the gating hysteresis of the C-terminal domain of MscCG provides the channel with gating properties highly suitable for release of intracellular solutes.