Thermosensor DesK Measures Membrane Thickness

CYBULSKI, L. E.; MARTÍN, M.; DE MENDOZA, D.

Baltimore

Congreso; 55th Annual Meeting Biophysical Society; 2011

The bacterium Bacillus subtilis adjusts the composition of membrane lipids to cope with temperature variations. The histidine kinase DesK is a five-pass transmembrane thermosensor suited to remodel membrane fluidity in Bacillus subtilis according to temperature. To understand the mechanism of sensing, individual transmembrane segments (TMS) were fused to the cytoplasmic catalytic domain of DesK (DesKC) and the ability to respond to temperature analyzed. Surprisingly, a hybrid TMS composed of 17 aminoacids of the first TMS and the C-terminal 14-residue portion of TM5 fused to DesKC, fully retains in vivo and in vitro the sensing properties of full-length DesK  [1]. Besides, when TMS1-DesKC or TMS5-DesKC is expressed in vivo individually, they are unresponsive to temperature. Nevertheless, when they are co-expressed thermosensing is recovered; suggesting that interactions between TMS1 and TMS5 are needed for signaling. The N-terminus of TMS1 contains three hydrophilic aminoacids near the lipid-water interface creating an instability hot spot. We showed that this boundary-sensitive motif controls the sensing and transmission activity. Accordingly, we hypothesize that membrane thickness is the temperature agent that determines the signaling state of the cold sensor by dictating the hydration level of the meta-stable hydrophilic spot. This hypothesis is supported through biochemical studies including in vitro reconstitution of the MS in liposomes with different chain length.