Quantitative Multiple-Reaction Monitoring Proteomic Analysis of Gß and Gγ Subunits in C57Bl6/J Brain Synaptosomes.

ABSTRACT

Gßγ dimers are one of the essential signaling units of activated G protein-coupled receptors (GPCRs). There are five Gß and 12 Gγ subunits in humans; numerous studies have demonstrated that different Gß and Gγ subunits selectively interact to form unique Gßγ dimers, which in turn may target specific receptors and effectors. Perturbation of Gßγ signaling can lead to impaired physiological responses. Moreover, previous targeted multiple-reaction monitoring (MRM) studies of Gß and Gγ subunits have shown distinct regional and subcellular localization patterns in four brain regions. Nevertheless, no studies have quantified or compared their individual protein levels. In this study, we have developed a quantitative MRM method not only to quantify but also to compare the protein abundance of neuronal Gß and Gγ subunits. In whole and fractionated crude synaptosomes, we were able to identify the most abundant neuronal Gß and Gγ subunits and their subcellular localizations. For example, Gß1 was mostly localized at the membrane while Gß2 was evenly distributed throughout synaptosomal fractions. The protein expression levels and subcellular localizations of Gß and Gγ subunits may affect the Gßγ dimerization and Gßγ-effector interactions. This study offers not only a new tool for quantifying and comparing Gß and Gγ subunits but also new insights into the in vivo distribution of Gß and Gγ subunits, and Gßγ dimer assembly in normal brain function.