Cell Biology

Sorting Out Rafts

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Science  29 May 2009:
Vol. 324, Issue 5931, pp. 1118
DOI: 10.1126/science.324_1118b

Yeast bud with secretory vesicles (red) and plasma membrane (blue).

CREDIT: KLEMM ET AL., J. CELL BIOL. 185, 601 (2009)

During membrane trafficking within eukaryotic cells, lipids and membrane-bound proteins are sorted and transported to their intracellular destinations, generating organelles with distinctive compositions of proteins and lipids. One major trafficking nexus is the trans-Golgi network (TGN), where proteins that have traversed the early stages of the secretory pathway are collected before transport to the plasma membrane. The plasma membrane is enriched in sphingolipids and sterols in comparison to internal membranes; how this sorting of lipid components occurs remains poorly understood, although lipid rafts—organized microdomains that include sterols, sphingolipids, saturated glycerophospholipids, and proteins—have been proposed to play a role.

Klemm et al. recovered post-Golgi secretory vesicles from yeast cells that had been modified so as to accumulate these vesicles in the bud. These vesicles were then subjected to a shotgun lipidomics procedure, which confirmed that the vesicles were enriched in ergosterol and sphingolipids. Thus, the TGN, in addition to acting as a sorting station for proteins, can indeed sort lipids. The vesicles also exhibited a more ordered lipid structure than the Golgi membrane, consistent with the idea that lipid rafts contribute to lipid sorting.

J. Cell Biol. 185, 601 (2009).

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