Background：

The small GTPases Rab are key regulators of intracellular membrane trafficking， from the formation of transport vesicles to their fusion with membranes. Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different set of downstream effectors directly responsible for vesicle formation， movement， tethering and fusion. The small Rab GTPase RAB11B plays a role in endocytic recycling， regulating apical recycling of several transmembrane proteins including cystic fibrosis transmembrane conductance regulator/CFTR， epithelial sodium channel/ENaC， potassium voltage-gated channel， and voltage-dependent L-type calcium channel. May also regulate constitutive and regulated secretion， like insulin granule exocytosis. Required for melanosome transport and release from melanocytes. Also regulates V-ATPase intracellular transport in response to extracellular acidosis.