Activation of the bacterial thermosensor DesK involves a serine zipper dimerization motif that is modulated by bilayer thickness

CYBULSKI L.E; BALLERING, J; MOUSSATOVA, A; INDA M.E; VAZQUEZ D.B; WASSENAAR T.A; DE MENDOZA, D.; TIELEMAN, D.P; KILLIAN JA

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Lugar: Washington DC, USA; Año: 2015 vol. 112 p. 6353 - 6358

0027-8424

DesK is a bacterial thermosensor protein involved in maintainingmembrane fluidity in response to changes in environmental temperature.Most likely, the protein is activated by changes in membranethickness, but the molecular mechanism of sensing andsignaling is still poorly understood. Here we aimed to elucidatethe mode of action of DesK by studying the so-called ?minimalsensor DesK? (MS-DesK), in which sensing and signaling are capturedin a single transmembrane segment. This simplified versionof the sensor allows investigation of membrane thickness-dependentprotein?lipid interactions simply by using synthetic peptides,corresponding to the membrane-spanning parts of functional andnonfunctional mutants of MS-DesK incorporated in lipid bilayerswith varying thicknesses. The lipid-dependent behavior of thepeptides was investigated by circular dichroism, tryptophan fluorescence,and molecular modeling. These experiments were complementedwith in vivo functional studies on MS-DesK mutants.Based on the results, we constructed a model that suggests a newmechanism for sensing in which the protein is present as a dimerand responds to an increase in bilayer thickness by membraneincorporation of a C-terminal hydrophilic motif. This results in exposureof three serines on the same side of the transmembranehelices of MS-DesK, triggering a switching of the dimerization interfaceto allow the formation of a serine zipper. The final result isactivation of the kinase state of MS-DesK.