Activation of the bacterial thermosensor DesK involves a serine zipper dimerization motif that is modulated by bilayer thickness.
DesK is a bacterial thermosensor protein involved in maintaining membrane fluidity in response to changes in environmental temperature. Most likely, the protein is activated by changes in membrane thickness, but the molecular mechanism of sensing and signaling is still poorly understood. Here we aimed to elucidate the mode of action of DesK by studying the so-called "minimal sensor DesK" (MS-DesK), in which sensing and signaling are captured in a single transmembrane segment. This simplified version of the sensor allows investigation of membrane thickness-dependent protein-lipid interactions simply by using synthetic peptides, corresponding to the membrane-spanning parts of functional and nonfunctional mutants of MS-DesK incorporated in lipid bilayers with varying thicknesses. The lipid-dependent behavior of the peptides was investigated by circular dichroism, tryptophan fluorescence, and molecular modeling. These experiments were complemented with in vivo functional studies on MS-DesK mutants. Based on the results, we constructed a model that suggests a new mechanism for sensing in which the protein is present as a dimer and responds to an increase in bilayer thickness by membrane incorporation of a C-terminal hydrophilic motif. This results in exposure of three serines on the same side of the transmembrane helices of MS-DesK, triggering a switching of the dimerization interface to allow the formation of a serine zipper. The final result is activation of the kinase state of MS-DesK.
Departamento de Microbiología and larisa.cybulski@gmail.com j.a.killian@uu.nl.
Larisa Estefanía
LE
Cybulski
Membrane Biochemistry and Biophysics, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands;
Joost
J
Ballering
Department of Biological Sciences and Centre for Biomolecular Simulation, University of Calgary, Calgary, Canada T2N 1N4; and.
Anastassiia
A
Moussatova
Departamento de Microbiología and.
Maria Eugenia
ME
Inda
Departamento de Microbiología and.
Daniela B
DB
Vazquez
Computational Biology, Department of Biology, University of Erlangen-Nürnberg, 91052 Erlangen, Germany.
Tsjerk A
TA
Wassenaar
Instituto de Biología Molecular y Celular de Rosario, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000 Rosario, Argentina;
Diego
D
de Mendoza
Department of Biological Sciences and Centre for Biomolecular Simulation, University of Calgary, Calgary, Canada T2N 1N4; and.
D Peter
DP
Tieleman
Membrane Biochemistry and Biophysics, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands; larisa.cybulski@gmail.com j.a.killian@uu.nl.
J Antoinette
JA
Killian
D020816:Amino Acid Motifs / Q000235:genetics; D002942:Circular Dichroism; D019281:Dimerization; D008051:Lipid Bilayers / Q000737:chemistry*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry / Q000235:genetics*; D015398:Signal Transduction / Q000502:physiology*; D013050:Spectrometry, Fluorescence; D013697:Thermosensing / Q000502:physiology*
D008051:Lipid Bilayers; D012694:Serine
helix–helix interaction; lipid–protein interaction; thermosensing; transmembrane helix dimerization; two-component system