Rabaptin4, a novel effector of the small GTPase rab4a, is recruited to perinuclear recycling vesicles.
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 GTPase 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. Rabaptin4 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 rab5a-binding site. Rabaptin4 is a cytosolic protein that inhibits the intrinsic 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.
Nagelkerken
B
B
Department of Cell Biology, Utrecht University School of Medicine, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
Van Anken
E
E
Van Raak
M
M
Gerez
L
L
Mohrmann
K
K
Van Uden
N
N
Holthuizen
J
J
Pelkmans
L
L
Van Der Sluijs
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D017931:DNA Primers; D011992:Endosomes / Q000201:enzymology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism*
D002352:Carrier Proteins; D017931:DNA Primers; D008565:Membrane Proteins; C097227:RABEP1 protein, human; D011994:Recombinant Proteins; D033921:Vesicular Transport Proteins; D020695:rab4 GTP-Binding Proteins