Ras-related protein Rab-27B

RAB27B is a small GTPase that regulates intracellular membrane trafficking by cycling between inactive GDP-bound and active GTP-bound states to recruit downstream effectors responsible for vesicle formation, movement, tethering, and fusion (UniProt: O00194). The protein specifically regulates late endocytic pathway homeostasis, including endosomal positioning, maturation, and secretion, and facilitates NTRK2/TRKB axonal anterograde transport through association with KLC1 (UniProt: O00194).

In Alzheimer's Disease, RAB27B is downregulated in post-mortem AD brain tissue compared to age-matched controls (Chaparral AD proteomics), with a mean log2 fold-change of −0.41 across subcellular fractions measured by TMT-labeled quantitative proteomics. This downregulation may reflect impaired endocytic pathway function and reduced neurotrophin receptor trafficking in AD pathology, though the functional consequences require further investigation.