Phospholipase C-β3 and -β1 form homodimers, but not heterodimers, through catalytic and carboxyl-terminal domains

Phospholipase C-beta (PLC-beta) isoenzymes are key effectors in G protein-coupled signaling pathways. Prior research suggests that some isoforms of PLC-beta may exist and function as dimers. Using coimmunoprecipitation assays of differentially tagged PLC-beta constructs and size-exclusion chromatography of native PLC-beta, we observed homodimerization of PLC-beta 3 and PLC-beta 1 isoenzymes but failed to detect heterodimerization of these isoenzymes. Size-exclusion chromatography data suggest that PLC-beta 3 and PLC-beta 1 form higher affinity homodimers than PLC-beta 2. Evidence supportive of limited PLC-beta monomer-homodimer equilibrium appears at <= 100 nM. Further assessment of homodimerization status by coimmunoprecipitation assays with differentially tagged PLC-beta 3 fragments demonstrated that at least two subdomains of PLC-beta 3 are involved in dimer formation, one in the catalytic X and Y domains and the other in the G protein-regulated carboxyl-terminal domain. In addition, we provide evidence consistent with the existence of PLC-beta homodimers in a whole-cell context, using fluorescent protein-tagged constructs and microscopic fluorescence resonance energy transfer assays.