Structural and functional differences between two homologous mechanosensitive channels of Methanococcus jannaschii

We report the molecular cloning and characterization of MscMJLR, a second t ype of mechanosensitive (MS) channel found in the archaeon Methanococcus ja nnaschii, MscMJLR is structurally very similar to MscMJ, the MS channel of M.jannaschii that was identified and cloned first by using the TM1 domain o f Escherichia coli MscL as a genetic probe. Although it shares 44% amino ac id sequence identity and similar cation selectivity with MscMJ, MscMJLR exh ibits other major functional differences. The conductance of MscMJLR of sim ilar to2 nS is approximately 7-fold larger than the conductance of MscMJ an d rectifies with voltage. The channel requires similar to 18 kT for activat ion, which is three times the amount of energy required to activate MscMJ, but is comparable to the activation energy of Eco-MscL, Our study indicates that a multiplicity of conductance-wise and energetically well-tuned MS ch annels in microbial cell membranes may provide for cell survival by the seq uential opening of the channels upon challenge with different osmotic cues.