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MscCG, a mechanosensitive channel of  Corynebacterium glutamicum  provides a major export mechanism for glutamate in this Gram-positive bacterium, which has for many years been used for industrial production of glutamate and other amino acids. The functional characterization of MscCG is therefore, of great significance to understand its conductive properties for different amino acids. Here we report the first successful giant spheroplast preparation of  C. glutamicum  amenable to the patch clamp technique, which enabled us to investigate mechanosensitive channel activities of MscCG in the native membrane of this bacterium. Single channel recordings from these spheroplasts revealed the presence of three types of mechanosensitive channels, MscCG, MscCG2, and CgMscL, which differ largely from each other in their conductance and mechanosensitivity. MscCG has a relatively small conductance of ~340 pS followed by an intermediate MscCG2 conductance of ~1.0 nS and comparably very large conductance of 3.7 nS exhibited by CgMscL. By applying Laplace’s law, we determined that very moderate membrane tension of ~5.5 mN/m was required for half activation of MscCG compared to ~12 mN/m required for half activation of both MscCG2 and CgMscL. Furthermore, by combining the micropipette aspiration technique with molecular dynamics simulations we measured mechanical properties of the  C. glutamicum  membrane, whose area elasticity module of  K  A  ≈ 15 mN/m is characteristic of a very soft membrane compared to the three times larger area expansion modulus of  K  A  ≈ 44 mN/m of the more elastic  E. coli  membrane. Moreover, we demonstrate that the “soft” properties of the  C. glutamicum  membrane have a significant impact on the MscCG gating characterized by a strong voltage-dependent hysteresis in the membrane of  C. glutamicum  compared to a complete absence of the hysteresis in the  E. coli  cell membrane. We thus propose that MscCG has evolved and adapted as an MscS-like channel to the mechanical properties of the  C. glutamicum  membrane enabling the channel to specialize in transport of amino acids such as glutamate, which are major osmolytes helping the bacterial cells survive extreme osmotic stress.

Evolutionary specialization of MscCG, an MscS-like mechanosensitive channel, in amino acid transport in Corynebacterium glutamicum