SUMMARY In spite of the crucial role of heterotrimeric G proteins as molecular switches transmitting signals from G protein-coupled receptors, their selective manipulation with small molecule, cell-permeable inhibitors still remains an unmet challenge. Here, we report that the small molecule BIM-46187, previously classified as pan-G protein inhibitor, preferentially silences Gαq signaling in a cellular context-dependent manner. Investigations into its mode of action reveal that BIM traps Gαq in the empty pocket conformation by permitting GDP exit but interdicting GTP entry, a molecular mechanism not yet assigned to any other small molecule Gα inhibitor to date. Our data show that Gα proteins may be “frozen” pharmacologically in an intermediate conformation along their activation pathway and propose a pharmacological strategy to specifically silence Gα subclasses with cell-permeable inhibitors.

The endogenous neutral amino acid L-proline exhibits a variety of physiological and behavioral actions in the nervous system, highlighting the importance of accurately regulating its extracellular abundance. The L-proline transporter PROT (Slc6A7) is believed to control the spatial and temporal distribution of L-proline at glutamatergic synapses by rapid uptake of this amino acid into presynaptic terminals. Despite the importance of members of the Slc6 transporter family regulating neurotransmitter signaling and homeostasis in brain, evidence that PROT dysfunction supports risk for mental illness is lacking. Here we report the disruption of the PROT gene by homologous recombination. Mice defective in PROT displayed altered expression of glutamate transmission-related synaptic proteins in cortex and thalamus. PROT deficiency perturbed mouse behavior, such as reduced locomotor activity, decreased approach motivation and impaired memory extinction. Thus, our study demonstrates that PROT regulates behaviors that are needed to respond to environmental changes in vivo and suggests that PROT dysfunctions might contribute to mental disorders showing altered response choice following task contingency changes.

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