Close similarity of baculovirus-expressed n-chimaerin and protein kinase C alpha as phorbol ester receptors.

n-Chimaerin is a recently described phorbol ester receptor that shares homology in its N-terminal region with the cysteine-rich zinc finger domain of protein kinase C. We have expressed n-chimaerin in insect cells using the baculovirus system and have used the isolated, recombinant n-chimaerin to characterize phorbol ester binding and structure-activity relations, lipid requirements, and inhibitor sensitivity. We find that n-chimaerin expressed in the baculovirus system bound [3H]phorbol 12,13-dibutyrate with high affinity (0.17 +/- 0.01 nM). Although having only a single cysteine-rich zinc finger region compared to two for protein kinase C, n-chimaerin thus closely resembled protein kinase C alpha. n-Chimaerin was likewise virtually indistinguishable from protein kinase C alpha in phorbol ester structure-activity relations, in phospholipid requirements, and in inhibition of binding by sphingosine and calphostin C, protein kinase C inhibitors acting on the regulatory domain. We conclude that a number of typical approaches used to implicate protein kinase C in biological function in cells do not discriminate between the n-chimaerin and protein kinase C classes of phorbol ester receptors.