A novel Rab5 GDP/GTP exchange factor complexed to Rabaptin-5 links nucleotide exchange to effector recruitment and function.
The small GTPase Rab5 plays an essential role in endocytic traffic. Rab GDP dissociation inhibitor delivers Rab5 to the membrane, where a nucleotide exchange activity allows recruitment of an effector protein, Rabaptin-5. Here we uncovered a novel 60 kDa Rab5-binding protein, Rabex-5. Rabex-5 forms a tight physical complex with Rabaptin-5, and this complex is essential for endocytic membrane fusion. Sequencing of mammalian Rabex-5 by nanoelectrospray mass spectrometry and cloning revealed striking homology to Vps9p, a yeast protein implicated in endocytic traffic. Rabex-5 displays GDP/GTP exchange activity on Rab5 upon delivery of the GTPase to the membrane. This demonstrates that a soluble exchange factor coupled to a Rab effector translocates from cytosol to the membrane, where the complex stabilizes the GTPase in the active state.
Horiuchi
H
H
European Molecular Biology Laboratory, Heidelberg, Germany.
Lippé
R
R
McBride
H M
HM
Rubino
M
M
Woodman
P
P
Stenmark
H
H
Rybin
V
V
Wilm
M
M
Ashman
K
K
Mann
M
M
Zerial
M
M
D000818:Animals; D001921:Brain / Q000201:enzymology; D002352:Carrier Proteins / Q000235:genetics; D002417:Cattle; D003001:Cloning, Molecular; D003600:Cytosol / Q000737:chemistry / Q000201:enzymology; D011992:Endosomes / Q000737:chemistry / Q000201:enzymology; D005656:Fungal Proteins / Q000235:genetics; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins; D020696:rab5 GTP-Binding Proteins
D002352:Carrier Proteins; D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; C108382:RABGEF1 protein, human; D029701:Saccharomyces cerevisiae Proteins; C099285:VPS9 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins