RAB27A is a small GTPase that regulates multiple aspects of membrane trafficking and vesicle transport. The protein cycles between inactive GDP-bound and active GTP-bound forms to control vesicle formation, movement, and fusion with target membranes 1. RAB27A plays a critical role in exosome secretion, where it controls multivesicular body (MVE) docking at the plasma membrane and prevents their lysosomal degradation 23. In hepatocytes, RAB27A facilitates production of extracellular vesicles that can promote liver fibrosis and cancer metastasis 43. The protein is essential for cytotoxic granule exocytosis in lymphocytes, controlling both granule maturation and docking at immunological synapses 5. RAB27A also regulates insulin granule recycling in pancreatic beta-cells through stimulus-endocytosis coupling 6. Disease relevance includes Griscelli syndrome 2 and hemophagocytic lymphohistiocytosis, where RAB27A mutations cause granule trafficking defects 7. Additionally, RAB27A facilitates viral protein transport to the plasma membrane during influenza infection 8. The protein's role in exosome-mediated cellular waste disposal may contribute to aging regulation 9.