A Systematic Approach Towards Elucidation of the Mode of Action of a Bacterial Thermosensor

Abstract

The Bacillus subtilis membrane harbors the temperature sensing and signaling protein DesK. At low temperatures it triggers expression of a desaturase, which introduces double bonds into pre-existing phospholipids, thereby regulating membrane fluidity. Recently it was discovered [1] that both sensing and transmission of DesK, which has five transmembrane segments, can be captured into one single chimerical transmembrane segment, the so-called ‘minimal sensor’. This simple system offers excellent perspectives to study the molecular detail of a biologically very important mechanism. As a first step here we analyzed membranes of Bacillus subtilis grown at different temperatures with several biophysical techniques including 31P-NMR and Differential Scanning Calorimetry. We analyzed the membrane lipid headgroup and acyl chain composition and we identified transition temperature fluctuations related to the growth temperature. We found significant differences in membrane lipid composition and phase behavior for Bacillus subtilis membranes depending on growth temperatures. The next step is to synthesize the transmembrane segment of the minimal sensor and incorporate it in these membranes exploiting their properties to elucidate the molecular mechanism of thermosensing in Bacillus subtilis. [1] Cybulski LE, Martin M, Mansilla MC, Fernandez A, de Mendoza D. Membrane thickness cue for cold sensing in a bacterium. Curr Biol. 2010 20(17):1539-44