Plays a role in cytotoxic granule exocytosis in lymphocytes. Required for both granule maturation and granule docking and priming at the immunologic synapse.

Found in all the examined tissues except in brain. Low expression was found in thymus, kidney, muscle and placenta. Detected in melanocytes, and in most tumor cell lines examined. Expressed in cytotoxic T-lymphocytes (CTL) and mast cells.

Defects in RAB27A are a cause of Griscelli syndrome type 2 (GS2) [MIM:607624]. Griscelli syndrome is a rare autosomal recessive disorder that results in pigmentary dilution of the skin and hair, the presence of large clumps of pigment in hair shafts, and an accumulation of melanosomes in melanocytes. GS2 patients also develop an uncontrolled T-lymphocyte and macrophage activation syndrome, known as hemophagocytic syndrome, leading to death in the absence of bone marrow transplantation. Neurological impairment is present in some patients, likely as a result of hemophagocytic syndrome.

Belongs to the small GTPase superfamily. Rab family.

Membrane. Melanosome. Late endosome. Lysosome. Identified by mass spectrometry in melanosome fractions from stage I to stage IV. Localizes to endosomal exocytic vesicles.