Functionality and specific membrane localization of transport GTPases carrying C-terminal membrane anchors of synaptobrevin-like proteins.

Ras-related guanine nucleotide-binding proteins of the Ypt/Rab family fulfill a pivotal role in vesicular protein transport both in yeast and in mammalian cells. Proper functioning of these proteins involves their cycling between a GTP- and a GDP-bound state as well as their reversible association with specific membranes. Here we show that the yeast Ypt1 and Sec4 proteins, essential components of the vesicular transport machinery, allow unimpaired vesicular transport when permanently fixed to membranes by membrane-spanning domains replacing their two C-terminal cysteine residues. Membrane detachment of the GTPases therefore is not obligatory for transport vesicle docking to or fusion with an acceptor membrane. It was also found that the membrane anchors derived from different synaptobrevin-related proteins have targeting information and direct the chimeric GTPases to different cellular compartments, presumably from the endoplasmic reticulum via the secretory pathway.