The DesK-DesR phosphorylation cascade controls the membrane lipid fluidity in Bacillus subtilis

CYBULSKI L.E; ALBANESI, D; MANSILLA, MC; DE MENDOZA

Iguazú, Argentina

Congreso; XL Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2004

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

The Des pathway of Bacillus subtilis regulates the synthesis of the cold-shock induced membrane-bound enzyme D5-fatty acid desaturase (D5-Des), which introduces double bonds into phospholipids acyl chains. This pathway is uniquely and stringently regulated by a two-component system composed of a membrane-associated kinase, DesK, and a soluble transcriptional activator, DesR. We demonstrated that DesK is a bifunctional enzyme with both kinase and phosphatase activities, that could assume different signaling states in response to changes in membrane fluidity. We also studied the mechanism by which the sensor protein DesK controls the level of phosphorylation of its cognate partner, DesR. We found that only the phosphorylated form of protein DesR is able to bind to a regulatory region immediately upstream of the promoter of the D5-Des gene (Pdes). Phosphorylation of the regulatory domain of dimeric DesR promotes, in a cooperative fashion, the hierarchical occupation of two adjacent, non identical, DesR-P DNA binding sites, so that there is a shift in the equilibrium toward the tetrameric active form of the response regulator. Subsequently, this phosphorylation signal propagation leads to the activation of the des gene through recruitment of RNA polymerase to Pdes. This is the first dissected example of a phosphorylation-activated cascade for a cold-shock gene, allowing the cell to optimize the fluidity of membrane phospholipids.