Proc. Natl. Acad. Sci. USA doi:10.1073/pnas.1317147111

Many bacteria are able to adjust the fluidity of their lipid membranes in response to changes in external temperature. For example, when Bacillus subtilis experience low temperatures, the histidine kinase DesK phosphorylates DesR, which then activates the transcription of a fatty acid desaturase; this desaturase catalyzes the formation of double bonds in the membrane lipids, thereby restoring membrane fluidity. At higher temperatures, DesK acts as a phosphatase, removing the phosphate group from phospho-DesR to halt the transcription of the desaturase. Inda et al. now report that a highly conserved stretch of positively charged amino acids, found between the thermosensor-containing transmembrane (TM) domain and the cytoplasmic catalytic domain of DesK, adopts distinct conformations in response to temperature-dependent changes in the thickness of the lipid membrane. When the temperature decreases, the conformation of this 'linker region' changes from a disordered, membrane-associated peptide to a helical structure that can enter the lipid bilayer to form a continuous α-helix with the TM domain. Disruption of this continuous α-helix (i.e., at higher temperatures) leads to conformational changes in the cytoplasmic catalytic domain of DesK, switching it from a kinase to a phosphatase. Similar mechanisms may be used to help regulate the activity of transient receptor potential channels, mechanosensitive channels and other membrane proteins.