MECHANOSENSITIVE ION CHANNELS OF THE ARCHAEON HALOFERAX-VOLCANII

Mechanosensitive (MS) ion channels have been documented in a variety o f cells belonging to Eukarya and Eubacteria. We report the novel findi ng of two types of MS ion channels in the cell membrane of the halophi lic archaeon Haloferax volcanii, a member of the Archaea that comprise the third phylogenetic domain. The two channels, MscA1 and MscA2, dif fered in their kinetic properties with MscA1 exhibiting more frequent open-closed transitions than MscA2. Both channels have large conductan ces that rectify between -40 mV and +40 mV where the conductance of Ms cA1 ranged from 380 to 680 picosiemens, whereas MscA2 ranged from 850 to 490 picosiemens. Both channels were blocked by submillimolar gadoli nium. In addition, the channels of either membrane vesicles or deterge nt-solubilized membrane proteins remained functional upon reconstituti on into artificial liposomes, a result that indicates that these chann els are activated by mechanical force transmitted via the lipid bilaye r alone. Subsequently a 37-kDa protein corresponding to the MscA1 chan nel activity was purified. With the possible functional similarity to bacterial MS channels, our finding of MS channels in Archaea emphasize s the ubiquity and importance of these channels in all domains of the evolutionary tree.