Javitch J A, Fu D, Chen J, Karlin A
Center for Molecular Recognition, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Neuron. 1995 Apr;14(4):825-31. doi: 10.1016/0896-6273(95)90226-0.
The binding site of the dopamine D2 receptor, like that of other homologous G protein-coupled receptors, is contained within a water-accessible crevice formed among its seven membrane-spanning segments. We have developed a method to map systematically all the residues forming the surface of this binding-site crevice, and we have applied this method to the third membrane-spanning segment (M3). We mutated, one at a time, 23 residues in and flanking M3 to cysteine and expressed the mutant receptors heterologously. Ten of these mutants reacted with charged, hydrophilic, lipophobic, sulfhydryl-specific reagents, added extracellularly, and were protected from reaction by a reversible dopamine antagonist. Thus, the side chains of these residues are exposed in the binding-site crevice, which like M3 extends from the extracellular to the intracellular side of the membrane. The pattern of exposure is consistent with a short loop followed by six turns of an alpha helix.
多巴胺D2受体的结合位点，与其他同源G蛋白偶联受体的结合位点一样，位于其七个跨膜片段之间形成的一个水可及的裂隙内。我们开发了一种方法来系统地绘制构成该结合位点裂隙表面的所有残基，并且我们已将此方法应用于第三个跨膜片段（M3）。我们将M3及其侧翼的23个残基逐个突变为半胱氨酸，并异源表达突变受体。这些突变体中有十个与细胞外添加的带电荷、亲水性、疏脂性、巯基特异性试剂发生反应，并受到可逆性多巴胺拮抗剂的保护而不发生反应。因此，这些残基的侧链暴露在结合位点裂隙中，该裂隙与M3一样从膜的细胞外侧延伸至细胞内侧。暴露模式与一个短环后接α螺旋的六圈一致。
