科研之友
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摘要
The G(i/o) protein family transduces signals from a diverse group of G protein-coupled receptors (GPCRs). The observed specificity of G(i/o)-GPCR coupling and the high rate of G(i/o) signal transduction have been hypothesized to be enabled by the existence of stable associates between G(i/o) proteins and their cognate GPCRs in the inactive state (G(i/o)-GPCR preassembly). To test this hypothesis, we applied the recently developed technique of two-photon polarization microscopy (2PPM) to G alpha(i1) subunits labeled with fluorescent proteins and four GPCRs: the alpha(2A)-adrenergic receptor, GABA(B), cannabinoid receptor type 1 (CB1R), and dopamine receptor type 2. Our experiments with non-dissociating mutants of fluorescently labeled G alpha(i1) subunits (exhibiting impaired dissociation from activated GPCRs) showed that 2PPM is capable of detecting GPCR-G protein interactions. 2PPM experiments with non-mutated fluorescently labeled G alpha(i1) subunits and alpha(2A)-adrenergic receptor, GABA(B), or dopamine receptor type 2 receptors did not reveal any interaction between the G(i1) protein and the non-stimulated GPCRs. In contrast, non-stimulated CB1R exhibited an interaction with the G(i1) protein. Further experiments revealed that this interaction is caused solely by CB1R basal activity; no preassembly between CB1R and the G(i1) protein could be observed. Our results demonstrate that four diverse GPCRs do not preassemble with non-active G(i1). However, we also show that basal GPCR activity allows interactions between non-stimulated GPCRs and G(i1) (basal coupling). These findings suggest that G(i1) interacts only with active GPCRs and that the well known high speed of GPCR signal transduction does not require preassembly between G proteins and GPCRs.
- 出版日期2017-6-9
