B. Nagelkerken et al., Rabaptin4, a novel effector of the small GTPase rab4a, is recruited to perinuclear recycling vesicles, BIOCHEM J, 346, 2000, pp. 593-601
The small GTPase rab4a is associated with early endocytic compartments and
regulates receptor recycling from early endosomes. To understand how rab4a
mediates its function, we searched for proteins which associate with this G
TPase and regulate its activity in endocytic transport. Here we identified
rabaptin4, a novel effector molecule of rab4a. Rabaptin4 is homologous with
rabaptin5 and contains a C-terminal deletion with respect to rabaptin5, Ra
baptin4 preferentially interacts with rab4a-GTP and to a lesser extent with
rab5aGTP. We identified a rab4a-binding domain in the N-terminal region of
rabaptin4, and two binding sites for rab5, including a novel N-terminal ra
b5a-binding site. Rabaptin4 is a cytosolic protein that inhibits the intrin
sic GTP hydrolysis rate of rab4a and is recruited by rab4a-GTP to recycling
endosomes enriched in cellubrevin and internalized indocarbocyanine-3 (Cy3
)-labelled transferrin. We propose that rabaptin4 assists in the docking of
transport vesicles en route from early endosomes to recycling endosomes.