Figure 1. The structure of phorbol ester bound to the C1b domain of protein kinase C (PKC) delta is shown. The phorbol ester is portrayed as a ball-and-stick representation, with the carbon atoms in black and the oxygen atoms in red. The backbone of the zinc finger is indicated in grey. The four residues N7, S10, P11, and L20, which are present as arginines in PKC zeta and iota, are purple. The residues that hydrogen bond with the phorbol ester are in green (the hydrogen bonds are shown as green dotted lines), and the other positively charged residues are blue.