Membrane domains

Where's Ras?

Science's STKE  28 Jan 2003:
Vol. 2003, Issue 167, pp. tw42-TW42
DOI: 10.1126/stke.2003.167.tw42

Although specialized lipid domains, particularly lipid rafts, are recognized to be important in localization of signaling molecules, it has been difficult to assign proteins to particular domains, especially those that are not defined by morphological characteristics. Prior et al. used immunogold electron microscopy to visualize localization of Ras proteins labeled with green fluorescent protein at high resolution in membrane fragments from cultured cells. They also used statistical analysis to evaluate clustering of the Ras proteins and potential colocalization with reference marker proteins. These techniques even allow distinction between domains of inner and outer leaflets of the plasma membrane. Although inactive H-Ras was present in both lipid rafts and a separate cholesterol-independent domain, active H-Ras and K-Ras were found in nonoverlapping domains, both of which are distinct from rafts. Such distinct localization may account for the different signals produced by the structurally similar Ras proteins. The authors note that their technique may be generally useful for monitoring spatial organization of signaling proteins in the plasma membrane.

I. A. Prior, C. Muncke, R. G. Parton, J. F. Hancock, Direct visualization of Ras proteins in spatially distinct cell surface microdomains. J. Cell Biol. 160, 165-170 (2003). [Abstract] [Full Text]