Rab11-FIP2 functions in transferrin recycling and associates with endosomal membranes via its COOH-terminal domain.

Rab11-FIP2 is a recently described member of the Rip11/Rab11-FIP/Rab coupling protein family of Rab11 interacting proteins. Rab11-FIP2 interacts with both Rab11 and myosin Vb and co-localizes with Rab11 in both HeLa and Madin-Darby canine kidney cells (Hales, C. M., Griner, R., Hobdy-Henderson, K. C., Dorn, M. C., Hardy, D., Kumar, R., Navarre, J., Chan, E. K., Lapierre, L. A., and Goldenring, J. R. (2001) J. Biol. Chem. 276, 39067-390751). Here, we characterized the specificity of the interaction between Rab11-FIP2 and Rab11 and report that it does not interact with Rab4, Rab3, Rab5, Rab6, or Rab7. We demonstrate that the COOH-terminal region of Rab11-FIP2, which contains the Rab11 binding domain (RBD), is necessary and sufficient for its early endosomal membrane association. In contrast, the amino-terminal region, which contains a phospholipid binding C2-domain, by itself was insufficient for membrane binding. Expression of a deletion mutant of Rab11-FIP2, containing the RBD, caused tubulation of a transferrin receptor-positive early endosomal compartment in HeLa cells. Endogenous Rab11 was also associated with this compartment. This phenotype cannot be reversed by excess wild-type Rab11, or dominant-positive Rab11 (Rab11Q70L), suggesting that Rab11-FIP2 functions downstream of Rab11 in endosomal trafficking.