CONICET | Buscador de Institutos y Recursos Humanos

The Bacillus subtilis histidine kinase DesK is a paradigmatic example of thermosensitive integral membrane enzyme designed to promote its fluidity when temperature drops below ~30°C. A small chimera of 31aa of the transmembrane region has been probed to retain the thermosensor functionality in native and synthetic membranes [Curr.Biol. 20:15391544, 2010]. To untangle the mechanism behind the thermosensor function of the chimera region, we performed Molecular Dynamics simulations of this peptide in DMPC bilayers at 25°C and 37°C, temperatures below and above the threshold for the enzyme activity change. At T=25°C the chimera secondary structure shows a large alpha helix segment starting at residue 8 from the N- through the C-terminus. The N-terminus 10aa segment, rich in basic residues, lays nearly parallel to the polar region of the lipid bilayer. At 37°C the alpha helix secondary structure survive only for two small 4aa segments.We have also simulated point mutants (K10L, N12L, H5+ in low pH conditions), which in experimental assays have lead to a reduction of the kinase activity at low temperature. In all cases we found that the original wild type alpha helix structure is disrupted by the mutations. For the mutant (L11K) which has an enhanced experimental activity at low temperature, we found that the main segment of alpha helix is conserved in the secondary structure, although it did not survive to the high temperature conditions.We have analyzed other structural variables like the atomic depth profile of the residues relative to the membrane groups, its interactions with solvent and lipid polar groups, and helix parameters to understand the transduction of the signal to the cytoplasmic catalytic portion of the enzyme.