Rab11b is essential for recycling of transferrin to the plasma membrane

Members of the Rab family of small GTPases play important roles in membrane trafficking along the exocytic and endocytic pathways. The Rab subfamily c onsists of two highly conserved members, Rab11a and Rab11b. Rab11a has been localized both to the pericentriolar recycling endosome and to the transGo lgi network and functions in recycling of transferrin. However, the localiz ation and function of Rab11b are completely unknown. In this study green fl uorescent protein (G;FP)-tagged Rab11b was used to determine its subcellula r localization. GFP-Rab11b colocalized with internalized transferrin, and u sing different mutants of Rabllb, the role of this protein in transferrin u ptake and recycling was examined. Two of these mutants, Rab11b-Q/L (constit utively active) and Rab11b-S/N (constitutively inactive), strongly inhibite d the recycling of transferrin. Interestingly, both of them had no effect o n transferrin uptake. In contrast, the C-terminally altered mutant Rab11b-D elta C, which cannot be prenylated and therefore cannot interact with membr anes, did not interfere with wildtype Rabllb function. From these data we c oncluded that functional Rabllb is essential for the transport of internali zed transferrin from the recycling compartment to the plasma membrane, (C) Academic Press.