Identification of GABAc Receptor Protein Homeostasis Network Components from Three Tandem Mass Spectrometry Proteomics Approaches

gamma-Amino butyric acid type C (GABA(c)) receptors inhibit neuronal firing primarily in retina. Maintenance of GABA(c) receptor protein homeostasis in cells is essential for its function. However, a systematic study of GABA(c) receptor protein homeostasis (proteostasis) network components is absent. Here coimmunoprecipitation of human GABA(c)-rho 1-receptor complexes was performed in HEK293 cells overexpressing rho l receptors. To enhance the coverage and reliability of identified proteins, immunoisolated rho 1-receptor complexes were subjected to three tandem mass spectrometry (MS)based proteomic analyses, namely, gel-based tandem MS (GeLC-MS/MS), solution-based tandem MS (SoLC-MS/MS), and multidimensional protein identification technology (MudPIT). From the 107 identified proteins, we assembled GABA(c)-rho 1-receptor proteostasis network components, including proteins with protein folding, degradation, and trafficking functions. We studied representative individual rho 1-receptor-interacting proteins, including calnexin, a lectin chaperone that facilitates glycoprotein folding, and LMAN1, a glycoprotein trafficking receptor, and global effectors that regulate protein folding in cells based on bioinformatics analysis, including HSF1, a master regulator of the heat shock response, and XBP1, a key transcription factor of the unfolded protein response. Manipulating selected GABA(c) receptor proteostasis network components is a promising strategy to regulate GABA(c) receptor folding, trafficking, degradation and thus function to ameliorate related retinal diseases.