Intramolecular allosteric interaction in the phospholipase C-δ1 pleckstrin homology domain

Protein activities are generally regulated by intramolecular allosteric interactions, by which spatially separated sites in a protein molecule communicate. Intramolecular allosteric interactions in the phospholipase C (PLC)-δ1 pleckstrin homology (PH) domain were investigated by solution NMR spectroscopy for selectively [α-(15)N]Lys-labeled proteins. The results of NMR analyses indicated that the binding of inositol 1,4,5-trisphosphate (IP3) to the protein induces local environmental changes at all lysine residues, including residues such as Lys-43 spatially separated from the specific IP3 binding site consisting of Lys-30, Lys-32, and Lys-57. IP3 binding also induces conformational stabilization of a characteristic short α-helix (α2) from residues 82 to 87. Mutational analyses indicated that an interaction network mainly consisting of the side chains of Lys-30, Lys-32, and Lys-43 exists in the ligand-free protein, and it was therefore predicted that binding of IP3 to the specific site modifies the interaction network, resulting in formation of a new interaction network, in which the side chains of Lys-57 and Phe-87 contribute to stable IP3 binding. These results provide evidence for intramolecular interactions in the PLC-δ1 PH domain, the function of which could be allosterically regulated by modifications at sites spatially separated from the ligand-binding site through the intramolecular interaction network.