MOLECULAR MECHANISM FOR THE ACTIVATION OF DESR FROM Bacillus subtilis

ALBANESI, DANIELA; TRAJTENBERG, FELIPE; RUETALO, NATALIA; CYBULSKI, LARISA; BOTTI, HORACIO; MECHALY, ARIEL; DE MENDOZA, DIEGO; BUSCHIAZZO, ALEJANDRO

Rosario

Congreso; IX Congreso de Microbiología General; 2013

Sociedad Argentina de Microbiología General

Temperature sensing is essential for the survival of living cells. A major challenge is to understand how thermal information is processed by a biological thermometer to optimize cellular functions. In bacteria, the most studied system leading to thermal adaptation is the Des pathway of Bacillus subtilis which is composed of the DesK/DesR two-component system (TCS) and D5-Des, a D5-acyl desaturase encoded by the des gene. The DesK/DesR TCS functions as a molecular thermosensor that responds to temperature variations to regulate fatty acid desaturation metabolism. Induction of the Des pathway is brought about by the ability of the histidine kinase DesK to assume different signaling states in response to variations in membrane fluidity. An increase in the proportion of ordered membrane lipids favors a kinase-dominant state of DesK, which undergoes autophosphorylation and then transfers the phosphate to the response regulator DesR. DesR-P binds to the des promoter inducing des transcription. Once synthesized, D5-Des introduces double bonds in the acyl chains of membrane lipids decreasing the transition temperature of the phospholipids. A more fluid membrane favors the phosphatase activity of DesK on DesR-P turning off des transcription. Here we determine through structural, biochemical and in vivo studies the molecular mechanism leading to the activation of DesR upon phosphorylation. We show that unphosphorylated DesR is a monomer exhibiting a closed conformation that inhibits dimer formation. Phosphorylation at the active site promotes conformational changes that are propagated throughout the receiver domain, promoting the opening of a hydrophobic pocket that is essential for homodimer formation and enhanced DNA-binding activity. The detailed understanding of this modulation mechanism provides unique opportunities to learn how the activity of response regulators from TCSs is modulated, an aspect that has remained elusive until now, and also to comprehend how Gram-positive bacteria adjust the membrane lipid composition according to its physical state.