A maize FK506-sensitive immunophilin, mzFKBP-66, is a peptidylproline cis-trans-isomerase that interacts with calmodulin and a 36-kDa cytoplasmic protein

A member of a eukaryotic gene superfamily, encoding a peptidylproline cis-trans-isomerase (rotamase) has been isolated from a maize (Zea mays L. A69Y +) endosperm cDNA library. The maize sequence (mzFKBP-66) encodes a 66-kDa polypeptide most closely related to the subclass of rotamases which bind an immunosuppressive drug, FK506, (termed FK506-binding proteins, FKBPs), and possesses four tandem copies of the FKBP-like binding domain. The sequence mzFKBP-66 is expressed ubiquitously in the maize plant, and the protein encoded is present in both cytosolic and nuclear compartments within the cell. Both the native mzFKBP-66 and a recombinant protein overexpressed in Escherichia coli showed peptidylproline cis-trans-isomerase (PPIase) activity at rates comparable to those reported for mammalian immunophilins. This activity was also sensitive to inhibition by FK506. Immunoaffinity chromatography using anti-mzFKBP66 demonstrated an association of the protein with an unknown 36-kDa polypeptide, and affinity chromatography of mzFKBP-66 on calmodulin-agarose beads indicated the presence of a calmodulin-binding site. The existence of mzFKBP-66-associated proteins suggests that plant immunophilins may act as part of multicomponent complexes, as has been shown for other representatives of this class of enzyme.