Mechanism of membrane fluidity optimization: isothermal control of the Bacillus subtilis acyl-lipid desaturase.

CYBULSKI, L.; ALBANESI, D.; MARIA CECILIA MANSILLA; ALTABE, S.; AGUILAR, P. S.; DE-MENDOZA, D.

MOLECULAR MICROBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2002 vol. 45 p. 1379 - 1388

0950-382X

The Des pathway of Bacillus subtilis regulates the expression of the acyl-lipid desaturase, Des, thereby controlling the synthesis of unsaturated fatty acids (UFAs) from saturated phospholipid precursors. Previously, we showed that the master switch for the Despathway is a two-component regulatory system composed of a membrane-associated kinase, DesK, and a soluble transcriptional regulator, DesR, which stringently controls transcription of the des gene. Activation of this pathway takes place when cells are shifted to low growth temperature. Here, we report on the mechanism by which isoleucine regulates the Despathway. We found that exogenous isoleucine sources, as well as its α -keto acid derivative, which is a branched-chain fatty acid precursor, negatively regulate the expression of thedes gene at 37 ° C. The DesK?DesR two-component system mediates this response, as both partners are required to sense and transduce the isoleucine signal at 37°C. Fatty acid profiles strongly indicate that isoleucine affects the signalling state of the DesK sensor protein by dramatically increasing the incorporation of the lower-melting-point anteiso-branched-chain fatty acids into membrane phospholipids. We propose that both a decrease in membrane fluidity at constant temperature and a temperature downshift induce des by the same  mechanism. Thus, the Des pathway would provide a novel mechanism to optimize membrane lipid fluidity at a constant temperature.