Biochemical characterization of the minor immunophilins

Objective: We present biochemical characterization of the previously described 14 kDa, 37 kDa, and 52 kDa immunophilins and a newly identified 5–8 kDa immunophilin. Design and methods: Proteins were tested for the following enzymatic activities—rotamase, G3PDH, protein kinase C, cAMP dependent protein kinase—and for the ability to inhibit calcineurin phosphatase when complexed with tacrolimus (FK506). Results: The 5–8 kDa protein, like the other minor immunophilins, lacks rotamase activity. Since the 37 kDa possesses G3PDH activity, the 5–8 kDa protein, 14 kDa protein, and 52 kDa protein were all tested and found to lack G3PDH activity. Additional work shows that none of the minor immunophilins possess protein kinase C or cyclic AMP-dependent protein kinase activity and that the 37 kDa and 5–8 kDa and probably the 52 kDa proteins are capable of inhibiting calcineurin phosphatase when bound to tacrolimus.