FK506-binding protein 15

FK506-binding protein 15 (FKBP15) is a 1219-amino-acid protein with putative roles in neuronal cytoskeletal organization and endosomal transport. Although structurally related to immunophilin family members, FKBP15 appears catalytically inactive as a peptidyl-prolyl isomerase. It is implicated in coordinating the transition between microfilament- and microtubule-based vesicular movement, particularly at early endosomes (UniProt: Q5T1M5).

The protein localizes to neuronal growth cones and is involved in processes fundamental to axonal development and synaptic function. No disease associations are documented in the UniProt record for FKBP15.

FKBP15 shows elevated abundance in Alzheimer's disease brain tissue. Quantitative proteomics of post-mortem AD brain versus age-matched controls detected an upregulation of FKBP15 with a mean log2 fold-change of +0.346 across subcellular fractions (Chaparral AD proteomics). This increase may reflect compensatory cytoskeletal remodeling or endosomal dysfunction associated with neurodegeneration, though the functional consequence remains to be established.