华支睾吸虫线粒体苹果酸脱氢酶基因的原核表达及重组蛋白的功能鉴定

目的克隆肝吸虫线粒体苹果酸脱氢酶基因并在大肠杆菌内表达,同时对表达的重组蛋白进行初步的功能分析,为进一步的研究和药物筛选打下基础。方法通过大规模测序从肝吸虫cDNA文库中确定肝吸虫线粒体苹果酸脱氢酶基因,采用PCR方法扩增出目的片段,与表达质粒pGEX-4T-1连接构建重组质粒,IPTG诱导表达;研究重组蛋白的理化性质及酶动力学特征,并寻找可能的抑制剂。结果成功表达出约64 kDa的重组蛋白,凝血酶切后为36 kDa蛋白,其酶活性为63.6U/mg。1.14 mM 4,4′-二甲氨基联苯甲醇处理30 min酶活性下降了60%;吡喹酮、灭滴灵和阿苯哒唑对酶活性无抑制作用;而5’-单磷酸腺苷对重组酶有竞争性抑制作用,其Ki为0.49。结论成功地表达了目的蛋白,为药物筛选提供了一个易于获得的候选蛋白分子。     

福建省禽流感病毒非结构蛋白基因特征分析

目的 明确福建省不同亚型不同源的禽流感病毒非结构蛋白基因(non-structural gene, NS)的遗传进化关系及氨基酸变异特征。方法 将2011年分离的毒株A/Chicken/Fujian/FZ04/2011(H9N2)(FZ-04株)、A/Chicken/Fujian/FZ11/2011(H9N2)(FZ-11株)的NS基因,与GenBank上登录的1997-2011年福建省不同源不同亚型的AIV毒株及国内外代表株的NS基因进行序列比对和遗传进化分析。结果 FZ-04和FZ-11株与福建省AIV的NS基因同源性分别为88.2%～99.0%,88.3～99.4%。福建省H5N1亚型毒株均属于Y439亚群,H9N2亚型毒株均属于Y280亚群。福建仅H5N1毒株的NS1蛋白80-84位有5个氨基酸缺失,且在羧基末端存在ESEV/GSEV两种PL基序,这可能是福建省区分高致病性和低致病性禽流感病毒的标志之一。结论 NS基因的特征分析表明,福建省H9N2毒株没有向高致病性H5N1毒株突变的嗜性,为今后进一步分析福建省禽流感病毒的NS基因遗传进化关系及毒力变异提供科学依据。     

寨卡病毒包膜蛋白Y158H突变对乙脑/寨卡嵌合病毒感染小鼠脑内神经毒力的影响北大核心CSCD

目的研究乙脑/寨卡嵌合病毒(Japanese encephalitis/Zika chimeric virus,JE/ZIKV)包膜蛋白(envelope protein,E蛋白)第158位氨基酸Y158H突变对感染小鼠脑内神经毒力的影响。方法运用重叠延伸PCR技术和基因克隆技术构建含Y158H突变全长cDNA的质粒,单酶切形成线性化DNA分子后体外转录获得RNA,电转染BHK21细胞完成重组病毒包装。通过病毒基因测序、间接免疫荧光试验、生长曲线及蚀斑试验鉴定病毒,通过动物试验评价病毒的小鼠脑内神经毒力。结果基因测序和酶切证实,成功构建含突变位点Y158H全长cDNA质粒。蚀斑试验和病毒基因测序、间接免疫荧光试验证实成功完成病毒的拯救,JE/ZIKV蚀斑直径(1.7±0.2)mm,JE/ZIKV(Y158H)蚀斑直径(1.6±0.1)mm,两种病毒的蚀斑大小差异无统计学意义(P>0.05)。两种病毒增殖规律相似,但整个过程中JE/ZIKV(Y158H)的增殖效率略低于母本病毒。分别用两种病毒进行动物试验,JE/ZIKV(Y158H)的LD50为58.93 PFU/0.03 ml,JE/ZIKV为2.21 PFU/0.03 ml,JE/ZIKV(Y158H)的毒力低于JE/ZIKV。结论ZIKV E蛋白Y158H位点突变可降低嵌合病毒对小鼠脑内神经毒力,E158是影响E蛋白神经毒力的重要氨基酸之一。     

寨卡病毒包膜蛋白Y158H突变对乙脑/寨卡嵌合病毒感染小鼠脑内神经毒力的影响

目的研究乙脑/寨卡嵌合病毒(Japanese encephalitis/Zika chimeric virus, JE/ZIKV)包膜蛋白(envelope protein, E蛋白)第158位氨基酸Y158H突变对感染小鼠脑内神经毒力的影响。方法运用重叠延伸PCR技术和基因克隆技术构建含Y158H突变全长cDNA的质粒,单酶切形成线性化DNA分子后体外转录获得RNA,电转染BHK21细胞完成重组病毒包装。通过病毒基因测序、间接免疫荧光试验、生长曲线及蚀斑试验鉴定病毒,通过动物试验评价病毒的小鼠脑内神经毒力。结果基因测序和酶切证实,成功构建含突变位点Y158H全长cDNA质粒。蚀斑试验和病毒基因测序、间接免疫荧光试验证实成功完成病毒的拯救,JE/ZIKV蚀斑直径(1.7±0.2)mm, JE/ZIKV(Y158H)蚀斑直径(1.6±0.1)mm,两种病毒的蚀斑大小差异无统计学意义(P0.05)。两种病毒增殖规律相似,但整个过程中JE/ZIKV(Y158H)的增殖效率略低于母本病毒。分别用两种病毒进行动物试验,JE/ZIKV(Y158H)的LD_(50)为58.93 PFU/0.03 ml, JE/ZIKV为2.21 PFU/0.03 ml, JE/ZIKV(Y158H)的毒力低于JE/ZIKV。结论 ZIKV E蛋白Y158H位点突变可降低嵌合病毒对小鼠脑内神经毒力,E158是影响E蛋白神经毒力的重要氨基酸之一。     

安徽省人感染H7N9禽流感病毒基因组特征分析

目的 分析安徽省2013年分离的5株人感染H7N9禽流感病毒全基因组特征。方法 从美国国家生物技术信息中心(NCBI)和全球禽流感基因共享数据库(GISAID)中下载具有代表性的H7N9、H7N3、H7N7和H9N2等毒株序列,运用分子生物信息学软件分析病毒全基因组特征。结果 我省流行的H7N9病毒HA基因与A/duck/Fujian/6390/2010(H7N3)相似度最高,NA基因与A/northern shoveler/Hong Kong/MPL133/2010(H2N9)株相似度最高,6个内部基因片段与中国北京、香港、湖南、江苏地区分离的H9N2毒株相似度接近。氨基酸序列比对发现NS1蛋白218~230位氨基酸缺失、M2蛋白的N31S突变、HA蛋白的G186V 、Q226L突变以及NA蛋白69~73位的删除,并且我省人感染H7N9病毒均带有PB2的E627K突变,同时PA-100A、PA-356R、PA-409N这些易感人类的特征氨基酸也在本次流行的H7N9病毒中发现;此外HA蛋白裂解位点仅有1个碱性氨基酸、糖基化位点高度保守以及未发现NA蛋白R294K突变也是我省H7N9病毒主要特征。结论 我省人感染H7N9病毒与中国其他省份流行株高度同源,该病毒获得跨种传播、毒力增强、耐药等能力均与病毒蛋白功能域有关。     

上调Yes相关蛋白对缺氧复氧心肌细胞损伤保护作用的实验研究

目的研究Yes相关蛋白(YAP)在缺氧复氧(H/R)心肌细胞损伤中的作用。方法用过表达YAP重组慢病毒感染心肌细胞,给予H/R处理,用real-time PCR和Western blot检测细胞中YAP表达情况。CCK8法测定增殖变化,二硝基苯肼显色法检测乳酸脱氢酶(LDH)漏出率,流式细胞术检测凋亡变化,Western blot检测活化型Caspase-3和Caspase-9蛋白水平,DCFH-DA法检测活性氧(ROS)水平,黄嘌呤氧化法检测超氧化物歧化酶(SOD)活性,JC-1法检测线粒体膜电位,Western blot法检测胞浆和线粒体中细胞色素C(Cytochrome C)蛋白水平。结果过表达YAP重组慢病毒感染可以提高H/R条件下心肌细胞中YAP表达水平。H/R处理后的心肌细胞增殖活性降低,LDH漏出率升高,细胞凋亡率升高,细胞中活化型Caspase-3和Caspase-9蛋白水平升高,ROS水平也升高,SOD活性降低,线粒体膜电位下降,胞浆中Cytochrome C蛋白水平升高,线粒体中Cytochrome C蛋白水平降低。上调YAP可以提高H/R条件下心肌细胞增殖活性,降低LDH漏出率,减少细胞凋亡,降低细胞中活化型Caspase-3和Caspase-9蛋白水平表达,提高SOD活性,减少细胞中ROS水平,提高线粒体膜电位,降低胞浆中Cytochrome C蛋白水平,提高线粒体中Cytochrome C蛋白水平。结论上调YAP减轻缺氧复氧心肌细胞损伤,减少细胞凋亡,作用机制可能与提高抗氧化酶活性,减少细胞内ROS水平,抑制线粒体凋亡途径有关。     

结核分枝杆菌katG基因突变对异烟肼耐药性的影响

目的探讨结核分枝杆菌katG基因突变TGG328TTT(Trp328Phe)对异烟肼耐药性的影响。方法以结核分枝杆菌标准株H37Rv和临床突变株DNA为模板,采用PCR扩增野生型和双突变型(含Trp328Phe与Met420Thr)katG基因,采用重叠延伸PCR技术构建单突变型(Trp328Phe)katG基因。将各katG基因重组至质粒pET22b(+),再导入表达宿主菌BL21(DE3)pLySs中,IPTG诱导目的蛋白表达,亲和层析法对重组KatG蛋白进行分离纯化。通过各重组KatG蛋白与过氧化氢和邻联大茴香胺反应,检测受试菌过氧化氢酶和过氧化物酶的活性。结果成功获得纯化的KatG蛋白。相比野生型KatG(19.05U/mg和7.05×10-3 U/mg),单突变型KatG(10.50U/mg和2.23×10-3 U/mg)过氧化氢酶和过氧化物酶活性分别下降44.9%和68.3%,双突变型KatG(11.88U/mg和3.31×10-3 U/mg)则分别下降37.6%和53.0%。结论 katG基因(Trp328Phe)突变引起KatG酶活性部分缺失,与异烟肼耐药有关,可作为耐药菌株基因检测的标志用于基因芯片的开发。双突变时KatG蛋白活性较高,提示katG-328TTT具有代偿性突变的作用。     

亚洲牛带绦虫36kDa胞浆型苹果酸脱氢酶基因的表达、纯化及免疫学分析

目的对亚洲牛带绦虫胞浆型苹果酸脱氢酶基因(malate dehydrogenase,MDH)进行克隆、表达和免疫学研究。方法将亚洲牛带绦虫成虫MDH克隆到原核表达质粒pET-30a(+)中,在大肠埃希菌BL-21/DE3中用IPTG诱导表达,表达产物通过十二烷基磺酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)进行鉴定,用镍离子金属螯合剂亲和层析柱进行纯化,纯化的重组蛋白用蛋白印迹(Western Blotting)进行免疫学分析。结果PCR、双酶切及DNA测序结果均表明pET-30a(+)-TaMDH重组质粒构建成功。SDS-PAGE结果表明目的基因在大肠埃希菌BL-21/DE3中获得高效表达,经亲和层析获得了高纯度蛋白。重组蛋白可被其免疫的SD大鼠血清识别,表明其具有免疫原性;并且能识别感染了亚洲牛带绦虫的猪血清,表明其具有免疫反应性。结论亚洲牛带绦虫苹果酸脱氢酶基因可在原核表达系统中获得具有免疫学活性的高效表达,为进一步研究该蛋白的功能奠定了基础。     

结核分枝杆菌KatG-ACT271CCT(Thr271Pro)突变与异烟肼耐药关系的研究

目的 探讨结核分枝杆菌katG ACT271CCT(Thr271Pro)基因点突变对异烟肼耐药性的影响方法 应用基因克隆技术合成野生型katG、突变型katG(AGC315ACC)和katG(ACT271CCT)基因片段,分别重组至质粒pET22b(+),转入表达菌BL21(DE3)pLySs,IPTG诱导目的蛋白表达,亲和层析法对目的蛋白分离纯化。最终检测重组katG蛋白过氧化物酶及过氧化氢酶活性。此外,通过软件AutoDock4.0采用半柔性对接方式分别模拟野生型katG蛋白、Thr271Pro突变型katG蛋白与异烟肼相互作用结果 成功获得纯化katG重组蛋白。相比野生型katG蛋白(过氧化氢酶活性361.5 U/mg和过氧化物酶活性77.6 U/mg),Thr271Pro突变型katG蛋白过氧化氢酶和过氧化物酶活性分别下降56%和63%(158.8 U/mg和28.7 U/mg),而Ser315Thr突变型katG蛋白过氧化氢酶和过氧化物酶活性分别下降74%和75%(96.2 U/mg和19.7 U/mg)。分子对接结果提示,异烟肼与Thr271Pro突变型katG蛋白结合自由能较野生型升高,Thr271Pro突变蛋白与异烟肼结合的亲和性降低。271位氨基酸突变后, Thr271Pro突变型katG蛋白氧化反应活性空腔发生一定的变形结论 katG Thr271Pro基因突变引起katG蛋白酶活性部分缺失和氧化反应活性空腔发生变形,导致异烟肼耐药。     

一株南宁市人源高致病H7N9禽流感病毒全基因组特性分析

目的通过全基因组序列分析南宁市1株人感染高致病H7N9禽流感病毒的分子遗传特性。方法不明原因肺炎患者1例,采集其下呼吸道痰液,经荧光RT-PCR检测H7N9核酸阳性后送中国疾病预防控制中心分离病毒并应用illumina平台深度测序,用MEGA5.1进行同源性和重要氨基酸位点分析,采用Neighbor-Joining法构建进化树。结果分离毒株命名为A/Nanning/01/2017(H7N9),测序分析该毒株的8个基因与A/chicken/Heinan/ZZ01/2017(H7N9)和A/Guangdong/HP001/2017(H7N9)高度同源。其中,HA蛋白裂解位点由PEIPKGR↓GLF突变为PEVPKRKRTAR↓GLF,具有高致病性的分子特征;受体结合位点G186V发生变异,毒力相关位点D225G发生突变,糖基化位点保守,飞沫传播关键氨基酸158D/224K/226L、110Y/160A/226L/228S和196R/226L/228S任一组合未发生突变。NA蛋白茎杆区丢失5个氨基酸,糖基化位点和耐药性位点保守。M2蛋白耐药性位点V27G和S31N发生突变。PB1蛋白I368V位点,PA蛋白K356R位点,M1蛋白N30D位点和T215A位点及NS1蛋白P42S位点均发生突变。PB2蛋白关键氨基酸位点E627K和D701N未突变。结论生物信息学分析A/Nanning/01/2017(H7N9)毒株可能来源于珠三角地区禽类的感染,具有高致病性禽流感病毒的分子特征,但未发现二代传播,人传人的可能性不大。该毒株对神经氨酸酶抑制剂药类敏感,对M2离子通道抑制剂可能产生耐药性。     

Mutational analysis of yeast vacuolar H(+)-ATPase.

Yeast mutants in which genes encoding subunits of the vacuolar H(+)-ATPase were interrupted were assayed for their vacuolar ATPase and proton-uptake activities. The vacuoles from the mutants lacking subunits A (72 kDa), B (57 kDa), or c (proteolipid, 16 kDa) were completely inactive in these reactions. Immunological studies revealed that in the absence of each one of those subunits the catalytic sector was not assembled. Labeling with N,N'-[14C]dicyclohexylcarbodiimide showed the presence of the proteolipid in vacuoles of mutants in which genes encoding subunits of the catalytic sectors were interrupted. No labeling was detected in the mutant in which the gene encoding the proteolipid was interrupted. We conclude that of all the ATPase subunits only the proteolipid is assembled independently and it serves as a template for the assembly of the other subunits. Site-specific mutations were generated in the gene encoding the proteolipid. All of the drastic changes and replacements gave inactive proteins. About half of the single amino acid replacements gave active proteins. Replacing glutamic acid-137 by any of several amino acids, except for aspartic acid, abolished the activity of the enzyme. Other amino acids that may function in proton conductance were changed. It was found that glycine residues may replace amino acids with exchangeable protons.     

An engineered Escherichia coli tyrosyl-tRNA synthetase for site-specific incorporation of an unnatural amino acid into proteins in eukaryotic translation and its application in a wheat germ cell-free system

Tyrosyl-tRNA synthetase (TyrRS) from Escherichia coli was engineered to preferentially recognize 3-iodo-L-tyrosine rather than L-tyrosine for the site-specific incorporation of 3-iodo-L-tyrosine into proteins in eukaryotic translation systems. The wild-type TyrRS does not recognize 3-iodo-L-tyrosine, because of the bulky iodine substitution. On the basis of the reported crystal structure of Bacillus stearothermophilus TyrRS, three residues, Y37, Q179, and Q195, in the L-tyrosine-binding site were chosen for mutagenesis. Thirty-four single amino acid replacements and 16 of their combinations were screened by in vitro biochemical assays. A combination of the Y37V and Q195C mutations changed the amino acid specificity in such a way that the variant TyrRS activates 3-iodo-L-tyrosine 10-fold more efficiently than L-tyrosine. This engineered enzyme, TyrRS(V37C195), was tested for use in the wheat germ cell-free translation system, which has recently been significantly improved, and is now as productive as conventional recombinant systems. During the translation in the wheat germ system, an E. coli suppressor tRNA(Tyr) was not aminoacylated by the wheat germ enzymes, but was aminoacylated by the E. coli TyrRS(V37C195) variant with 3-iodo-l-tyrosine. After the use of the 3-iodotyrosyl-tRNA in translation, the resultant uncharged tRNA could be aminoacylated again in the system. A mass spectrometric analysis of the produced protein revealed that more than 95% of the amino acids incorporated for an amber codon were iodotyrosine, whose concentration was only twice that of L-tyrosine in the translation. Therefore, the variant enzyme, 3-iodo-L-tyrosine, and the suppressor tRNA can serve as an additional set orthogonal to the 20 endogenous sets in eukaryotic in vitro translation systems.     

Active amino acids of the Kell blood group protein and model of the ectodomain based on the structure of neutral endopeptidase 24.11

In addition to its importance in transfusion, Kell protein is a member of the M13 family of zinc endopeptidases and functions as an endothelin-3-converting enzyme. To obtain information on the structure of Kell protein we built a model based on the crystal structure of the ectodomain of neutral endopeptidase 24.11 (NEP). Similar to NEP, the Kell protein has 2 globular domains consisting mostly of alpha-helical segments. The domain situated closest to the membrane contains both the N- and C-terminal sequences and the enzyme-active site. The outer domain contains all of the amino acids whose substitutions lead to different Kell blood group phenotypes. In the model, the zinc peptidase inhibitor, phosphoramidon, was docked in the active site. Site-directed mutagenesis of amino acids in the active site was performed and the enzymatic activities of expressed mutant Kell proteins analyzed and compared with NEP. Our studies indicate that Kell and NEP use the same homologous amino acids in the coordination of zinc and in peptide hydrolysis. However, Kell uses different amino acids than NEP in substrate binding and appears to have more flexibility in the composition of amino acids allowed in the active site.     

Effect of single amino acid replacements on the thermal stability of the NH2-terminal domain of phage lambda repressor.

The thermal stabilities of mutant phage lambda repressors that have single amino acid replacements in the NH2-terminal domain have been studied by means of circular dichroism and differential scanning calorimetry. The variations in stability determined by these physical methods correlate with the resistance to proteolysis at various temperatures and can be compared with the temperature-sensitive activity of the mutants in vivo. In general, mutant proteins bearing solvent-exposed substitutions have thermal stabilities identical to wild type, whereas buried substitutions reduce stability. In one case, a single amino acid replacement increases the thermal stability of the repressor.     

An experimental approach to testing modular evolution: directed replacement of alpha-helices in a bacterial protein.

We have used oligonucleotide site-directed mutagenesis to ask whether certain structural motifs in proteins are determined mainly by local interactions among amino acids. Multiple consecutive amino acids in three alpha-helices in the alkaline phosphatase (EC 3.1.3.1) of Escherichia coli have been replaced with helical sequences from four other sources. Altogether, 12 distinct helical replacements were created, 9 of which retain enzymatic activity. Most short stretches of helical sequence can be replaced with unrelated helical sequences without eliminating enzyme activity. Replacements of the carboxyl half of an alpha-helix are less harmful than those of the amino half, and the two together are synergistic rather than additive. These results are consistent with the hypothesis that proteins originally evolved by the assembly of small functional folding units.     

Uncoupling of the DNA topoisomerase and replication activities of an initiator protein.

The replication initiator proteins encoded by the pT181 and related plasmids have sequence-specific DNA binding and topoisomerase activities. These proteins create a site-specific nick in one strand of the DNA at the origin of replication that serves as a primer for the initiation of replication. To define the regions of the pT181-encoded initiator protein, RepC, that are involved in its DNA binding, topoisomerase, and replication activities, we have carried out site-directed mutagenesis of the repC gene. Analysis of mutant RepC proteins in vitro and in vivo has identified the amino acids that are critical for its various biochemical activities. The DNA binding domain of RepC was found to be located near its C-terminal region and was different from the domain involved in its sequence-specific topoisomerase activity. These studies also showed that the DNA topoisomerase activity of the initiator protein can be uncoupled from its tight noncovalent DNA binding and replication activities.     

Selectivity of the cleavage/attachment site of phosphatidylinositol-glycan-anchored membrane proteins determined by site-specific mutagenesis at Asp-484 of placental alkaline phosphatase.

Many proteins are now known to be anchored to the plasma membrane by a phosphatidylinositol-glycan (PI-G) moiety that is attached to their COOH termini. Placental alkaline phosphatase (PLAP) has been used as a model for investigating mechanisms involved in the COOH-terminal processing of PI-G-tailed proteins. The COOH-terminal domain of pre-pro-PLAP provides a signal for processing during which a largely hydrophobic 29-residue COOH-terminal peptide is removed, and the PI-G moiety is added to the newly exposed Asp-484 terminus. This cleavage/attachment site was subjected to an almost saturation mutagenesis, and the enzymatic activities, COOH-terminal processing, and cellular localizations of the various mutant PLAP forms were determined. Substitution of Asp-484 by glycine, alanine, cysteine, asparagine, or serine (category I) resulted in PI-G-tailed and enzymatically active proteins. However, not all category I mutant proteins were PI-G tailed to the same extent. Pre-pro-PLAP with other substituents at position 484 (threonine, proline, methionine, valine, leucine, tyrosine, tryptophan, lysine, glutamic acid, and glutamine; category II) were expressed, as well as the category I amino acids, but there was little or no processing to the PI-G-tailed form, and this latter group exhibited very low enzyme activity. The bulk of the PLAP protein produced by category II mutants and some produced by category I mutants were sequestered within the cell, apparently in the endoplasmic reticulum (ER). Most likely, certain amino acids at residue 484 are preferred because they yield better substrates for the putative "transamidating" enzyme. In transfected COS cells, at least, posttranslational PI-G-tail processing does not go to completion even for preferred substrates. Apparently PI-G tailing is a requisite for transport from the ER and for PLAP enzyme activity. Proteins that are not transamidated are apparently retained in the ER in an inactive conformation.     

Role of group-conserved residues in the helical core of beta2-adrenergic receptor

G protein-coupled receptors (GPCRs) belonging to class A contain several highly conserved (>90%) amino acids in their transmembrane helices. Results of mutational studies of these highly conserved residues suggest a common mechanism for locking GPCRs in an inactive conformation and for their subsequent activation upon ligand binding. Recently, a second set of sites in the transmembrane helices has been identified in which amino acids with small side chains, such as Gly, Ala, Ser, Thr, and Cys, are highly conserved (>90%) when considered as a group. These group-conserved residues have not been recognized as having essential structural or functional roles. To determine the role of group-conserved residues in the beta(2)-adrenergic receptor (beta(2)-AR), amino acid replacements guided by molecular modeling were carried out at key positions in transmembrane helices H2-H4. The most significant changes in receptor expression and activity were observed upon replacement of the amino acids Ser-161 and Ser-165 in H4. Substitution at these sites by larger residues lowered the expression and activity of the receptor but did not affect specific binding to the antagonist ligand dihydroalprenolol. A second site mutation, V114A, rescued the low expression of the S165V mutant. Substitution of other group-conserved residues in H2-H4 by larger amino acids lowered receptor activity in the order Ala-128, Ala-76, Ser-120, and Ala-78. Together these data provide comprehensive analysis of group-conserved residues in a class A GPCR and allow insights into the roles of these residues in GPCR structure and function.