GAINING INSIGHTS INTO THE CONFORMATIONAL DYNAMICS OF PHOSPHOLIPASE C-BETA

Phospholipase Cs (PLCs) are a family of enzymes that hydrolyze membrane lipid phosphatidylinositol-4,5-bisphosphate (PIP2) to generate inositol triphosphate (IP3) and diacylglycerol (DAG). These second messengers activate a variety of intracellular responses, including inflammation, vascular smooth muscle contraction, and cardiac hypertrophy. While much is known about how Gaq-mediated activation of PLCb occurs, the same cannot be said for Gbg-mediated activation. Residues within the PLCb-Gbg binding interface were previously identified in interior regions of the protein, suggesting the PH domain must undergo a conformational change to allow for Gbg-mediated activation. However, the role of PH domain conformational dynamics in Gbg-mediated activation of PLCb has yet to be determined. In this work, I discuss efforts to characterize conformational dynamics of the PLCb PH domain and its role in interactions of the enzyme with liposomes and Gbg. First, I generated a disulfide crosslink between the PH domain and EF hands1/2 of PLCb3, purified under oxidizing or reducing conditions, and conducted biochemical and structural tests to determine any differences in structure and/or function of the protein as compared to wild-type. Results of these studies provided the first direct structural evidence of PLCb PH domain dynamics in solution. Then, I discuss the rationale behind the generation of a surface cysteine-less PLCb for use in solvatochromic fluorescence assays in the presence and absence of liposomes and Gbg. Initial results of these studies suggest the PLCb PH domain favors a buried conformation alone and in the presence of Gbg or liposomes, and likely exists at an equilibrium between open and closed states.