Résumé
Mechanosensitive (MS) ion channels have been documented in a variety of cells belonging to Eukarya andEubacteria. We report the novel finding of two types of MS ion channels in the cell membrane of the halophilic archaeonHaloferax volcanii, a member of the Archaeathat comprise the third phylogenetic domain. The two channels, MscA1 and MscA2, differed in their kinetic properties with MscA1 exhibiting more frequent open-closed transitions than MscA2. Both channels have large conductances that rectify between −40 mV and +40 mV where the conductance of MscA1 ranged from 380 to 680 picosiemens, whereas MscA2 ranged from 850 to 490 picosiemens. Both channels were blocked by submillimolar gadolinium. In addition, the channels of either membrane vesicles or detergent-solubilized membrane proteins remained functional upon reconstitution into artificial liposomes, a result that indicates that these channels are activated by mechanical force transmitted via the lipid bilayer alone. Subsequently a 37-kDa protein corresponding to the MscA1 channel activity was purified. With the possible functional similarity to bacterial MS channels, our finding of MS channels inArchaea emphasizes the ubiquity and importance of these channels in all domains of the evolutionary tree.