The function of ENSG00000069966 (GNB5, G protein subunit beta 5) is as follows. Enhances GTPase-activating protein (GAP) activity of regulator of G protein signaling (RGS) proteins, such as RGS7 and RGS9, hence involved in the termination of the signaling initiated by the G protein-coupled receptors (GPCRs) by accelerating the GTP hydrolysis on the G-alpha subunits, thereby promoting their inactivation (PubMed:27677260). Increases RGS7 GTPase-activating protein (GAP) activity, thereby regulating mood and cognition (By similarity). Increases RGS9 GTPase-activating protein (GAP) activity, hence contributes to the deactivation of G protein signaling initiated by D(2) dopamine receptors (PubMed:27677260). May play an important role in neuronal signaling, including in the parasympathetic, but not sympathetic, control of heart rate (By similarity). {ECO:0000250|UniProtKB:A1L271, ECO:0000250|UniProtKB:P62881, ECO:0000269|PubMed:27677260}.