Structural and mechanistic insights into the association of PKCα-C2 domain to PtdIns(4,5)Pâ

C2 domains are widely-spread protein signaling motifs that in classical PKCs act as Ca²⁺-binding modules. However, the molecular mechanisms of their targeting process at the plasma membrane remain poorly understood. Here, the crystal structure of PKCα-C2 domain in complex with Ca²⁺, 1,2-dihexanoyl-sn-glycero-3-[phospho-L-serine] (PtdSer), and 1,2-diayl-sn-glycero-3-[phosphoinositol-4,5-bisphosphate] [PtdIns(4,5)P₂] shows that PtdSer binds specifically to the calcium-binding region, whereas PtdIns(4,5)P₂ occupies the concave surface of strands β3 and β4. Strikingly, the structure reveals a PtdIns(4,5)P₂-C2 domain-binding mode in which the aromatic residues Tyr-195 and Trp-245 establish direct interactions with the phosphate moieties of the inositol ring. Mutations that abrogate Tyr-195 and Trp-245 recognition of PtdIns(4,5)P₂ severely impaired the ability of PKCα to localize to the plasma membrane. Notably, these residues are highly conserved among C2 domains of topology I, and a general mechanism of C2 domain-membrane docking mediated by PtdIns(4,5)P₂ is presented.