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英译中，急，谢谢。
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The ECLs and amino termini of GPCRs, together with the extracellular halves of thetransmembrane helices, are believed to define the ligand-binding site of each receptor (44).Therefore, the ECLs play an important role in the overall pharmacology of any particularreceptor. In general, small molecule ligands are thought to bind deeper within the space createdby the transmembrane domain helices, whereas larger ligands such as peptides bind closer tothe membrane surface near the ECLs (54,55). Mutagenesis studies suggest that the β2AR bindsits ligand deep within the transmembrane helix bundle, which may be related to the observationthat the extracellular regions have a rather simple structure with short loops connectingtransmembrane helices II and III, and VI and VII (Figure 4A). ECL2, which links helices IVand V, has a somewhat more extensive architecture that is unanticipated. In contrast to theburied, β-sheet structure of this loop in rhodopsin (Figure 4B), ECL2 in β2AR is more exposedto the solvent and contains an extra helical segment. Additionally, there is an intra-loopdisulfide bond between Cys1844.76 and Cys1905.29 that may help stabilize the more exposedECL2. A second disulfide bond between Cys1915.30 and Cys1063.25 in helix III effectively tiesECL2 to the transmembrane core (56). The distal portion of ECL2 makes close contacts withECL1 and contains a glycosylation site at Asn1875.26 (57), which may serve to mask a groupingof aromatic residues on ECL1; in this construct, Asn1875.26 has been mutated to glutamate toaid in crystallization. 大神们帮忙翻译下，谢谢。 |
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genhunter
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莫墨: 金币+80, 翻译EPI+1, ★★★★★最佳答案, 谢谢 2015-05-28 12:13:05
莫墨: 金币+80, 翻译EPI+1, ★★★★★最佳答案, 谢谢 2015-05-28 12:13:05
| ECLS和G蛋白偶联受体的氨基末端，以及朝细胞外的一半的跨膜螺旋，被认为是确定每个受体的配体结合位点（44）。因此，ECLS所有受体药理特征起到重要作用。一般认为，小分子配体结合由跨膜结构螺旋域形成的，较深的位点，而较大的配体如肽结合近膜表面附近的ECLS（54,55）。突变研究表明，β2AR 与其配体在跨膜结构螺旋域深部结合，这可能与其细胞外区域结构较为简单, 只有几个短环连接跨膜螺旋II和III，和VI和VII（图4A）。链接螺旋IV和V的ECL2有未曾预料的，更延展构像。与类似的在视紫红质里被包埋的β-片状结构相反（图4B），在β2AR 里ECL2更为曝露到溶剂(环境), 并含有额外的螺旋片段。此外，还有一对环内二硫键位于cys1844.76和cys1905.29之间, 可能有助于稳定更为曝露的ECL2。第二对位于cys1915.30和cys1063.25之间的二硫键有效的将ECL2与跨膜螺旋核心连系在一齐（56）。ECL2的远端与ECL1紧密接触, 并在Asn1875.26含一个糖基化位点（57），这可能起到掩盖ECL1上一组芳香族残基的作用；在这个结构中，asn1875.26被突变为谷氨酸, 以帮助结晶。 |
2楼2015-05-28 11:04:00