Ras-related protein Rab-5A

RAB5A encodes a small GTPase that functions as a master regulator of early endocytic trafficking (UniProt: P20339). The protein cycles between inactive GDP-bound and active GTP-bound states to recruit effector proteins that mediate vesicle formation, transport, and fusion. RAB5A specifically drives fusion of plasma membranes with early endosomes and is essential for EGF and transferrin endocytosis, as well as recruitment of regulatory complexes like EEA1 and RABEP1 to early endosomal membranes.

RAB5A functions broadly in endosomal membrane trafficking pathways critical for cellular nutrient uptake and intracellular signaling. The protein also participates in exosomal release of cargo proteins and regulates apoptotic cell clearance through phagosome maturation. No disease associations are noted in the UniProt record for this protein.

In Alzheimer's disease, RAB5A is downregulated in post-mortem AD brain tissue relative to age-matched controls (Chaparral AD proteomics), with a mean log2 fold-change of −0.22 across analyzed subcellular fractions. This reduction in early endosomal trafficking capacity may contribute to impaired endocytic function and protein clearance mechanisms implicated in AD pathogenesis.