A MAIZE FK506-SENSITIVE IMMUNOPHILIN, MZFKBP-66, IS A PEPTIDYLPROLINECIS-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 may s L. A69Y +) endosperm cDNA library. The maize sequence (mzFKBP-66) en codes a 66-kDa polypeptide most closely related to the subclass of rot amases which bind an immunosuppressive drug, FK506, (termed FK506-bind ing proteins, FKBPs), and possesses four tandem copies of the FKBP-lik e 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 an d a recombinant protein overexpressed in Escherichia coli showed pepti dylproline cis-trans-isomerase (PPIase) activity at rates comparable t o those reported for mammalian immunophilins. This activity was also s ensitive to inhibition by FK506. Immunoaffinity chromatography using a nti-mzFKBP66 demonstrated an association of the protein with an unknow n 36-kDa polypeptide, and affinity chromatography of mzFKBP-66 on calm odulin-agarose beads indicated the presence of a calmodulin-binding si te. The existence of mzFKBP-66-associated proteins suggests that plant immunophilins may act as part of multicomponent complexes, as has bee n shown for other representatives of this class of enzyme.