Expression and characterization of maize ZBP14, a member of a new family of zinc-binding proteins

A maize gene (Mz2-12), with a deduced amino acid sequence similar to that of a protein kinase C (PKC) inhibitor from bovine brain, has been expressed in Escherichia coli and the protein (ZBP14) purified to homogeneity. The bovine protein was originally identified by Walsh's group and named PKC inhibitor-1 (PKCI-1). The recombinant maize protein (ZBP14) shares characteristics of bovine PKCI-1: it has similar secondary structure, is dimeric, and has a similar affinity for zinc. However, the maize ZBP14 had very little activity as an inhibitor of mammalian brain PKC, thus precluding zinc sequestration as the mechanism of inhibition. The biological role for the maize protein in plant kinase regulation is therefore unclear. In the presence of both maize ZBP14 and 14-3-3 protein (which inhibits PKC in the absence of diacylglycerol), the effects on PKC appeared to be synergistic.