The ability to osmoregulate is essential to survival. Van der Heide and Poolman cloned and reconstituted into liposomes the purified components of the osmoregulated ABC transporter (OpuA) from Lactococcus lactis. With an ATP-regenerating system inside the liposomes, the OpuA system was able to transport glycine betaine into the liposomes. The uptake was stimulated by a transmembrane osmotic gradient of either ionic or nonionic solutes. Furthermore, transport activity was stimulated by tetracaine, an amphiphile that alters membrane curvature, mimicking the membrane stress that occurs under hyperosmotic conditions. The data suggest that the two proteins of the OpuA system serve as both the osomosensor and the osmoregulator and that the osmotic gradient is sensed as changes in the membrane bilayer.
van der Heide, T., and Poolman, B. (2000) Osmoregulated ABC-transport system of Lactococcus lactis senses water stress via changes in the physical state of the membrane. Proc. Natl. Acad. Sci. U.S.A. 97: 7102-7106. [Abstract] [Full Text]