It Takes Two to Tango: Activation of Protein Kinase D by Dimerization

The recent discovery and structure determination of a novel ubiquitin‐like dimerization domain in protein kinase D (PKD) has significant implications for its activation. PKD is a serine/threonine kinase activated by the lipid second messenger diacylglycerol (DAG). It is an essential and highly conserved protein that is implicated in plasma membrane directed trafficking processes from the trans‐Golgi network. However, many open questions surround its mechanism of activation, its localization, and its role in the biogenesis of cargo transport carriers. In reviewing this field, the focus is primarily on the mechanisms that control the activation of PKD at precise locations in the cell. In light of the new structural findings, the understanding of the mechanisms underlying PKD activation is critically evaluated, with particular emphasis on the role of dimerization in PKD autophosphorylation, and the provenance and recognition of the DAG that activates PKD. Protein kinase D (PKD) senses the lipid second messenger diacylglycerol (DAG) and transduces the signal into downstream protein phosphorylation. A novel ubiquitin‐like domain is required for PKD dimerization and activation on membranes in the cell. This article reviews the structural and biochemical basis of PKD activation by DAG.