From Genome Biology 2001, 2(5), 3007.1-7.
The Rab GTPase family
Rab GTPases belong to the Ras superfamily and central regulators of vesicle budding, motility, docking and fusion. Rab proteins swich between GTP-bound and GDP-bound forms. The GTP-bound form is an active state, and the GDP-bound form is an inactive state.
There are many members; human have approximately 70 Rab GTPases, S. cerevisiae (11), C.elegans(29), D. melanogastor(26), P.falciparum(11).
In general, Rab GTPase differ most in their carboxil termini, which has been implicated in subcellular targeting, whereas regions involved in guanine-nucleotide binding are most conserved.
Within cells, they are localized to the cytosolic face of distinct intracellular membranes. Their reversible membrane localization depends on the post-translational modification of a cystein motif at the very carboxyl terminus (CXXX, CC, CXC, CCXX or CCXXX where X is any amino acid), with one or two highly hydrophobic geranylgeranyl groups.
A Rab escrot protein (REP) presents rabprotein to the geranylgeranyl transferase. REP can functions as a chaperone that keeps the hydrophobic, geranylgeranylated Rab soluble and delivers it to the appropriate membrane.