Molecular interactions of 3',5'-cyclic purine analogues with the binding site of retinal rod ion channels.
Molecular interactions of 3',5'-cyclic purine analogues with the binding site of retinal rod ion channels.
复制标题
3,5-环状嘌呤类似物与视网膜杆离子通道结合位点的分子相互作用。
DOI：
10.1021/bi00007a030
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发表时间：
1995
期刊：
影响因子：
2.9
通讯作者：
Tanaka,JC
中科院分区：
文献类型：
--
作者：
Scott,SP;Tanaka,JC
Revised Manuscript Received December 15, 1994s abstract: Photoreceptor outer segments transduce information about incoming light levels through a class of ion channels that respond directly to changes in cytosolic 3', 5'-cyclic guanosine monophosphate levels. A series of 3', 5'-cyclic purine analogues with alterations at Nl, C2, C6, or C8 positions was used to examine molecular interactions between the nucleotide and the channel. The maximal current activated by C2-altered analogues in excised membranepatches was less than the current activated by cGMP, and the K0. 5, the concentrationwhich activates 50% of the current in a patch, was increased. Nonpolar C8-substituted cAMP analogues activated more current than the parent cAMP with lower Ko. s values. This was in contrast to 8-amino-cAMP, which exhibited greatly reduced activity. The rank order of activity, based on K0. 5 values, for C8-cAMP substituents was as follows: 8-azido-> 8-methylamino-> 8-benzylamino-> cAMP> 8-bromo-> 8-hydroxy-» 8-amino-cAMP. 1 A^-Etheno-cAMP and A5-monobutyryl-cAMP activated a small fraction of the total possible current with high K0. 5 values. Other analogues with alterations at Nl or C6 positionsincluding A'-oxide-cAMP, 2-aminopurine riboside 3', 5'-monophosphate, and A6-monosuccinyl-cAMP do not bind to the channel, suggesting that interactions with the channel in this region are essential for binding. In order to help interpret thechanges in maximal current and K0. 5 values compared to cGMP, molecular models of the active analogues were constructed and then docked into a molecular model of the cyclic nucleotide binding site of the retinal channel. This model, proposed by Kumar and Weber [(1992) Biochemistry 31, 4643—4649], was based on the crystal structure of cAMP bound to catabolite activator protein. Our modeling showed that the analogues were sterically accommodated within the binding site. No hydrogen bonds were predicted between the purine rings of cAMP and the pocket; however, Phe 533 on the/35 strand was predicted to form weak electrostatic interactions with C6 substituents on both cAMP and cGMP. The importance of contacts in this region of the binding pocket is further emphasized by the inactive analogues, all of which are altered at Nl or C6.In the absence of experimentally determined structures to atomic resolution for ion channel proteins, channel agonists and antagonists have been used successfully to derive details of molecular architecture (Hille, 1992). One important class of ion channels found on sensory neurons transduces information detected by the neuron into an electrical signal. In retinal rods, incoming photons are detected by rhodopsin, and information about the light flux is relayedthrough a biochemical cascade which terminates in changes of cytosolic 3', 5'-cyclic GMP levels (Kaupp, 1991; Yau & Baylor, 1989). The retinal rod ion channels responding directly to changes in cGMP levels display a~ 50-fold preference for cGMP1
