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

Abstract

The membrane sensor and signalling protein DesK is involved in detecting temperature changes in the bacterium Bacillus subtillis. 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’. It was hypothesized that a group of hydrophilic amino acids flanking this transmembrane segment represents the molecular switch responsible for turning on and off the kinase state of DesK. This switch would be regulated by the extent of exposure of this group to the aqueous phase, which in turn would depend on membrane thickness. Here we tested this hypothesis by employing different biophysical approaches, using synthetic peptides corresponding to functional and non-functional mutants of the minimal sensor in artificial model membranes of phosphatidylcholines of varying thickness and at different temperatures. The results of these studies will be reported. [1] Cybulski et al., manuscript submitted.