THE TRANSITORY COMPLEX BETWEEN PHOTOEXCITED RHODOPSIN AND TRANSDUCIN - RECIPROCAL INTERACTION BETWEEN THE RETINAL SITE IN RHODOPSIN AND THE NUCLEOTIDE SITE IN TRANSDUCIN
THE TRANSITORY COMPLEX BETWEEN PHOTOEXCITED RHODOPSIN AND TRANSDUCIN - RECIPROCAL INTERACTION BETWEEN THE RETINAL SITE IN RHODOPSIN AND THE NUCLEOTIDE SITE IN TRANSDUCIN
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DOI：
10.1111/j.1432-1033.1989.tb15068.x
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发表时间：
1989-10-01
期刊：
影响因子：
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通讯作者：
CHABRE, M
中科院分区：
文献类型：
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作者：
BORNANCIN, F;PFISTER, C;CHABRE, M
在视觉转导级联的第一步中，光激发的视紫红质分子R * ret与携带GDP的转导素分子TGDP结合。R *-T相互作用导致T中核苷酸位点的开放，并通过允许GDP的释放来催化GDP/GTP交换。我们研究了T中核苷酸位点和视紫红质中视网膜位点的占有对R~*-T过渡复合物的影响。从结合的转导素释放的GDP消除后，复合物，命名为R * ret-Te（ret为视网膜存在，e为核苷酸位点空）几乎无限期地保持稳定在介质中，其离子组成接近生理。在这种复合物中，结合的Te保持与GDP或GTP相互作用的持久能力，并且与衰减为视蛋白和游离视网膜的游离R * ret相比，R * ret在光谱上保持在meta-II状态。因此，打开T中核苷酸位点的R *-T相互作用相反地阻断R * ret中的视网膜位点。在低离子强度介质中长时间孵育后，R * ret-Te复合物部分解离，但释放的Te随后无法重新结合GDP或GTP，即使在R * ret存在下也是如此;它可能是变性的。在通过高浓度的羟胺处理R * ret-Te复合物时，可以从视紫红质中除去视黄醛。Re-Te复合物保持稳定，复合的转导蛋白保持其结合GTP的能力。TGTP然后从Re解离。被释放的Re失去了与新的转导蛋白相互作用的能力。这些数据被纳入级联发展的讨论。我们强调，亲和力，即解离平衡常数，是不足以描述一个R * Ret分子引发的反应流。它依赖于一些关键的快速结合和解离过程，实际上对其他缓慢的过程不敏感，因此对仅表示动力学常数之比的亲和力值不敏感。R *-T相互作用对视紫红质中视网膜位点的影响类似于G蛋白结合对其激动剂的受体的表观亲和力的影响。
In the first step of the visual transduction cascade a photoexcited rhodopsin molecule, R*ret, binds to a GDP-carrying transducin molecule, TGDP. The R*-T interaction causes the opening of the nucleotide site in T and catalyzes the GDP/GTP exchange by allowing the release of the GDP. We have studied the influences on this R*-T transitory complex of the occupancies of the nucleotide site in T and the retinal site in rhodopsin. After elimination of the GDP released from the bound transducin, the complex, named R*ret-Te (ret for retinal present, e for nucleotide site empty) remains stabilized almost indefinitely in a medium whose ionic composition is close to physiological. In this complex the bound Te retains a lasting ability to interact with GDP or GTP, and R*ret remains spectroscopically in the meta-II state, by contrast with free R*ret which decays to opsin and free retinal. Hence the R*-T interaction which opens the nucleotide site in T conversely blocks the retinal site in R*ret. Upon prolonged incubation in a low-ionic-strength medium the R*ret-Te complex dissociates partially, but the liberated Te is then unable to rebind GDP or GTP, even in the presence of R*ret; it is probably denaturated. Upon treatment of the R*ret-Te complex by a high concentration of hydroxylamine, the retinal can be removed from the rhodopsin. The Re-Te complex remains stable and the complexed transducin keeps its capacity to bind GTP. TGTP then dissociates from Re. The liberated Re loses its capacity to interact with a new transducin. These data are integrated into a discussion of the development of the cascade. We stress that affinities, i.e. dissociation equilibrium constants, are insufficient to describe the flow of reactions triggered by one R*Ret molecule. It depends on a few critical rapid binding and dissociation processes, and is practically insensitive to other slow ones, hence to the values of affinities that express only the ratio of kinetics constants. The effect of the R*-T interaction on the retinal site in rhodopsin is analogous to the effect of the binding of a G-protein on the apparent affinity of a receptor for its agonist.