Rab5

Rab5 is a small GTPase localised to early endosomes. It regulates the fusion
between endocytic vesicles and early endosomes, as well as the homotypic
fusion between early endosomes (Olkkonen and Stenmark, 1997). The GTP-bound 
form of Rab5 is the active form in membrane fusion, and the expression of a 
GTPase-deficient mutant induces giant endosomes in cells (Stenmark et al., 1994). 
Rabaptin-5 (Stenmark et al., 1995) and EEA1 (Simonsen et al., 1998) are among the effector 
proteins recruited by GTP-bound Rab5. 

For further details about Rab5 and its effectors, see Marino Zerial's web page.



Selected references: 

Simonsen A, Lippé R, Christoforidis S, Gaullier J-M, Brech A, Callaghan JM, Toh B-H, 
Murphy C, Zerial M and Stenmark H (1998)  EEA1 links PI(3)K function to Rab5 regulation 
of endosome fusion. Nature 394: 494-498

Olkkonen V and Stenmark H (1997). Role of Rab GTPases in membrane traffic. 
Int. Rev. Cytol.176: 1-85

Stenmark H, Vitale G, Ullrich O and Zerial M (1995)  Rabaptin-5 is a direct 
effector of  the small GTPase Rab5 in endocytic membrane fusion. Cell 83, 423-432

Stenmark H, Parton RG, Steele-Mortimer O, Lütcke A, Gruenberg J and Zerial M (1994) 
Inhibition of rab5 GTPase activity stimulates membrane fusion in endocytosis. 
EMBO J. 13: 1287-1296