Lipid-Binding Regions within PKC-Related Serine/Threonine Protein Kinase N1 (PKN1) Required for Its Regulation.

Abstract

PKC-related serine/threonine protein kinase N1 (PKN1) is a protease/lipid-activated protein kinase that acts downstream of the RhoA and Rac1 pathways. PKN1 comprises unique regulatory, hinge region, and PKC homologous catalytic domains. The regulatory domain harbors two homologous regions, i.e., HR1 and C2-like. HR1 consists of three heptad repeats (HR1a, HR1b, and HR1c), with PKN1-(HR1a) hosting an amphipathic high-affinity cardiolipin-binding site for phospholipid interactions. Cardiolipin and C18:1 oleic acid are the most potent lipid activators of PKN1. PKN1-(C2) contains a pseudosubstrate sequence overlapping that of C20:4 arachidonic acid. However, the cardiolipin-binding site(s) within PKN1-(C2) and the respective binding properties remain unclear. Herein, we reveal (i) that the primary PKN1-(C2) sequence contains conserved amphipathic cardiolipin-binding motif(s); (ii) that trimeric PKN1-(C2) predominantly adopts a β-stranded conformation; (iii) that two distinct types of cardiolipin (or phosphatidic acid) binding occur, with the hydrophobic component playing a key role at higher salt levels; (iv) the multiplicity of C18 fatty acid binding to PKN1-(C2); and (v) the relevance of our lipid-binding parameters for PKN1-(C2) in terms of kinetic parameters previously determined for the full-length PKN1 enzyme. Thus, our discoveries create opportunities to design specific mammalian cell inhibitors that disrupt the localization of membrane-associated PKN1 signaling molecules.