Dissimilar phorbol ester binding properties of the individual cysteine-rich motifs of protein kinase D

Protein kinase D (PKD) is a serine/threonine kinase that binds phorbol esters in a phospholipid-dependent manner via a tandemly repeated cysteine-rich, zinc finger-like motif (the cysteine-rich domain, CRD). Here, we examined whether the individual cysteine-rich motifs of the CRD of PKD (referred to as cysl and cys2) are functionally equivalent in mediating phorbol ester binding both in vivo and in vitro. Our results demonstrate that the cysl and cys2 motifs of the CRD of PKD are functionally dissimilar, with the cys2 motif responsible for the majority of [3H]phorbol 12,13-dibutyrate (PDB) binding, both in vivo and in vitro.