THE PLECKSTRIN HOMOLOGY DOMAIN OF PHOSPHOLIPASE C-DELTA(1) BINDS WITHHIGH-AFFINITY TO PHOSPHATIDYLINOSITOL 4,5-BISPHOSPHATE IN BILAYER-MEMBRANES

The pleckstrin homology (PH) domain of phospholipase C-delta(1) (PLC-d elta(1)) binds to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P-2) i n phospholipid membranes with an affinity (K-a similar to 10(6) M(-1)) and specificity comparable to those of the native enzyme. PLC-delta(1 ) and its PH domain also bind inositol 1,4,5-trisphosphate, the polar head group of PI(4,5)P-2, with comparable affinity and approximately 1 :1 stoichiometry. A peptide corresponding to amino acids 30-43 of the PLC-delta(1) PH domain contains several basic residues predicted to bi nd PI(4,5)P-2, but binds weakly and with little specificity for PI(4,5 )P-2; hence the tertiary structure of the isolated PH domain is requir ed for high affinity PI(4,5)P-2 binding. Our PI(4,5)P-2 binding result s support the hypothesis that the intact PH domain, serving as' a spec ific tether, directs PLC-delta(1) to membranes enriched in PI(4,5)P-2 and permits the active site, located elsewhere in the protein, to hydr olyze multiple substrate molecules before this enzyme dissociates from the membrane surface.