Interaction between Pleckstrin Homology Domains and G Protein βγ-Subunits : Analyses of Kinetic Parameters by a Biosensor-Based Method

Pleckstrin homology (PH) domains, comprised of rather weakly conserved sequences of about 100 amino acid residues, are a protein motif found in many signaling and cytoskeletal proteins. PH domains have been shown to bind to the βγ subunits of heterotrimeric GTP-binding proteins (Gβγ), but the affinity of PH domains for Gβγ has not been quantitatively estimated in detail. To characterize the nature of the interaction between PH domains and Gβγ, its kinetic parameters were analyzed using a BIAcoreTM instrument. All PH domains tested (PH domains of ras-specific guanine nucleotide exchange factor (ras-GRF), phospholipase (PLC) γ1, and Son of sevenless protein (Sos)) appeared to bind to Gβ1γ2 with affinity constants KD of 0.108, 0.318, and 0.208 μM, respectively. The binding of PH domains to Gβγ was inhibited by preincubation of Gβγ with the GDP-bound but not the GTP-bound form of Giα. This study showed a high affinity interaction between PH domains and Gβγ and suggests a potential role of PH domains in Gβγ-mediated signal transduction in intact cells.