“Structural and functional characterization of DesK, the membrane fluidity sensor of Bacillus subtilis”

ALBANESI, D; BUSCHIAZZO, A; TRAJTENBERG, F; MARTÍN, M; MANSILLA, MC; HAOUZ A; DE MENDOZA D; ALZARI, P

Rosario

Congreso; V Congreso Argentino de Microbiología General. SAMIGE.; 2008

Bacillus subtilis, a gram-positive bacterium, frequently encounters stress conditions in its natural environment, the soil. In order to detect and respond to these stressful and variable conditions, it employs two-component signal transduction systems. The B. subtilis Des pathway is composed of the membrane Delta 5-acyl lipid desaturase, Delta 5-Des, and the two component system DesK/DesR. DesK is a histidine kinase located in the membrane and DesR is a cytoplasmatic response regulator that binds specifically to the Pdes promoter. Induction of the Des pathway is brought about by the ability of DesK to assume different signaling states in response to changes in membrane fluidity. This could be accomplished by regulating the ratio of kinase to phosphatase activities. An increase in the proportion of ordered membrane lipids favors a kinase-dominant state of DesK, which undergoes autophosphorylation followed by the transfer of the phosphate group to the cytoplasmic response regulator DesR. Phosphorylated DesR binds to Pdes and interacts specifically with the RNA polymerase to turn on des transcription. Activation of des results in the synthesis of Delta 5-Des, which introduces double bonds in the acyl chains of membrane lipids. These newly synthesized unsaturated fatty acids decrease the phase transition temperature of the phospholipids, favoring the phosphatase activity of DesK on DesR-P and turning off transcription. We undertook structural studies in order to characterize the signaling states corresponding to the autokinase, phosphotransfer and phosphatase activities associated with the cytoplasmic region of DesK and to gain further insights into the mechanism by which this sensor protein can adjust its signaling state in response to changes in membrane lipid fluidity. Here, we describe the crystal structure of the complete soluble domain of DesK in two conformational states. Structure-inspired hypotheses for the distinct catalytic mechanisms and for signal transduction through the membrane to the cytoplasmic domain will be discussed.