“A minimal sensor that responds to membrane fluidity”

CYBULSKI, LE; MARTIN M; MANSILLA MC; FERNÁNDEZ, A; DE MENDOZA, D

Carlos Paz, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2008

The B. subtilis DesKR two component system has been identified as the first system that senses changes in membrane lipid fluidity and responds accordingly. It is composed of a membrane histidin-kinase, DesK, a cytoplasmic response regulator, DesR, and the effector enzyme, delta5-desaturase. Under conditions of restricted membrane fluidity DesK phosphorylates DesR, enabling its binding to the desaturase promoter. A tetramer of phosphorylated DesR positioned on Pdes recruits the RNAPolymerase to increase the transcription of the acyl-lipid desaturase. This enzyme introduces double bonds into the acyl chains of membrane lipids to decrease its phase transition temperature. To obtain a simple system to study the sensing mechanism of DesK we constructed a series of fusion proteins composed of the cytoplasmic domain of DesK and one of several chimerical transmembrane segments (TMSs) envisioned as possessing the critical elements involved in sensing. One of these fusion proteins behaves as DesK wild type, so we called it DesK-Minimal Sensor (DesK-MS). The unique TMS of DesK-MS seems to harbor the essence of the functioning of a biological sensor, having the required elements to perceive and transmit the signal. The DesK-MS give us the opportunity to test our hypothesis on its mode of action by the construction of several site-directed mutants and analyze its behavior in vitro