TBOA 抑制谷氨酸转运体功能对戊四氮点燃癫痫模型的影响

目的:研究新型谷氨酸转运体抑制剂TBOA对戊四氮点燃癫痫的发生及神经病理作用,寻找治疗戊四氮点燃癫痫的新方法.方法:戊四氮慢性点燃方法进行造模,分为癫痫组和TBOA治疗组.TBOA治疗组造模前3d大鼠侧脑室注射TBOA,癫痫组侧脑室注射生理盐水.2周后处死大鼠,研究两组癫痫的发生率、海马及皮质的病理改变、神经元计数.结果:1d的癫痫发生率在癫痫组为87.5%,TBOA治疗组为40.6%,光镜显示TBOA治疗组的损害程度轻于癫痫组.l、3d时海马CAI区神经元计数癫痫组与TBOA治疗组比较差异有显著性(P＜0.01);5、7d时,癫痫组神经元计数少于TBOA治疗组(均P＜0.05).皮质区变化规律同海马CAI区.结论:早期应用谷氨酸转运体抑制剂TBOA能降低癫痫的发生率,并改善癫痫后神经病理损害.     

蛋白C基因C64W和F139V突变致蛋白C缺陷的分子机制研究

目的研究蛋白C（PC）基因C64W、F139V和K150缺失突变（K150d）致PC缺陷症的分子机制。方法构建PC基因野生型和突变体表达质粒（PCwt、PC C64W、PC F139V、PC K150d）并瞬时转染至COS-7细胞或CHO细胞，进行体外表达试验和细胞免疫荧光染色；用荧光实时PCR（real-time PCR）检测转染细胞PC mRNA表达量的改变；蛋白降解抑制实验检测突变蛋白在细胞内的降解途径；内糖苷酶-H（Endo H）酶切试验检测PC翻译后侧链糖化修饰。结果PC C64W未从转染细胞内分泌且在细胞内逐渐降解，PC F139V仅部分从细胞内分泌，大部分未分泌并在细胞内逐渐降解，PC K150d突变体蛋白的分泌未受突变的明显影响。real-time PCR结果显示，与野生型PC mRNA相比，突变体PC mRNA不降低；蛋白降解抑制实验显示，PC C64W和PC F139V通过蛋白酶体途径进行细胞内降解。Endo H酶切和转染细胞荧光染色显示，PC C64W和PC F139V主要位于前高尔基体。结论分泌障碍和细胞内降解是PC C64W和PC F139V导致PC缺陷症的原因，PC K150d对突变体蛋白的分泌无明显影响。     

结缔组织生长因子与自发性高血压大鼠心肌纤维化的相关性研究

目的:探讨结缔组织生长因子(C TG F)在高血压心肌纤维化发生发展中的作用。方法:本实验以14周龄雄性W K Y大鼠和SH R大鼠为研究对象,测量14周、28周大鼠尾动脉压,并对大鼠左室心肌C TG F、TG F-β1的表达用免疫组化法进行半定量分析;R T-PC R法检测C TG F、TG F-β1m R N A表达水平;M A SSO N染色法观察胶原形态,测量胶原容积分数(C V F)和血管周围胶原面积(PV C A)。结果:(1)SH R大鼠组C V F、PV C A明显高于W K Y大鼠组(P<0.01);(2)C TG F、TG F-β1及其m R N A在SH R组左室心肌的表达较W K Y组明显增强(P<0.05)。(3)相关分析表明,C TG F与TG F-β1(r=0.562,P<0.05)、C V F(r=0.715,P<0.01)、PV C A(r=0.786,P<0.01)呈正相关。结论:C TG F参与了SH R大鼠高血压心肌纤维化的病理过程。     

凝血因子Ⅻ活性的变化对深静脉血栓形成的影响

目的探讨凝血因子Ⅻ活性(FⅫ:C)的变化对纤维蛋白(原)溶解功能与深静脉血栓形成(DVT)的影响。方法采用一期法测定63例DVT患者和30例正常对照组的FⅫ:C,同时用发色底物法检测血浆纤溶酶原活性(PLG:A),酶联免疫法测定组织型纤溶酶原激活物抗原性(t-PA:Ag)、纤溶酶原激活物抑制剂-1抗原性(PAI-1:Ag)及免疫比浊法测定血浆D-二聚体(D-D)含量。结果DVT组FⅫ:C和PLG:A含量显著低于正常对照组(P<0.01),其中5例(7.9%)年龄<45岁的患者FⅫ:C低于正常对照组x--2s。PAI-1:Ag、D-D含量显著高于正常组(P<0.01)。t-PA:Ag含量与正常对照组无显著差异(P>0.05)。结论FⅫ:C下降易导致纤溶酶原内激活途径受抑制,DVT的形成与FⅫ:C降低有关。     

蛋白C抗凝系统在尿毒症维持性血液透析中的变化及意义

目的 :探讨血浆抗凝因子蛋白 C(PC)、蛋白 S(PS)及血栓调节蛋白 (TM)在尿毒症、凝血异常导致出血并发症中的作用。方法 :采用双抗夹心酶联免疫吸附法 (EL ISA)及发色底物法测定 4 5例尿毒症血液透析 (血透 )患者及正常对照组血浆 PC抗原 (PC:Ag)、PC活性 (APC)、血浆总 PS(TPS)、血浆游离 PS(FPS)及 TM含量。结果 :尿毒症患者 PC:Ag、TPS、FPS、TM和 D二聚体 (DD)含量及 APC明显高于正常对照组 (P<0 .0 5或P<0 .0 0 1) ;维持性血透患者血浆 APC、TPS、FPS及 DD血透后明显升高 (P<0 .0 5或 P<0 .0 0 1) ;TM血透后明显降低 (P<0 .0 0 1) ;有出血并发症者血浆 PC:Ag、FPS、DD含量及 APC明显升高 (P<0 .0 5或 P<0 .0 1)。结论 :尿毒症患者蛋白 C抗凝活性降低 ,与尿毒症时高凝倾向和血栓形成有关。血透可激活原本已处于高凝状态的凝血系统 ,使体内蛋白 C抗凝途径的抗凝活性增强。     

细胞外信号调节激酶通路抑制剂对完全弗氏佐剂致痛大鼠背根神经结中谷氨酸转运蛋白表达的影响

目的:观察细胞外信号调节激酶(ERK)通路抑制剂PD98059时完全弗氏佐剂(CFA)致痛大鼠脊髓背根神经结(DRG)中谷氨酸转运蛋白表达的影响.方法:24只大鼠随机分为对照组、单纯致痛组、PD1组和PD10组.疼痛模型采用大鼠足底注射CFA 100μL.对照组及单纯致痛组经椎管内给予二甲基亚砜(DMSO)10μL,每日2次.PD1组和PD10组分别经椎管内给予PD98059 1μg或10μg,每日2次.测定大鼠每日痛阈变化,3 d后RT-PCR法检测大鼠DRG内谷氨酸转运蛋白表达的变化.结果:注射CFA致痛后各组大鼠痛阈均显著降低,PD1组与PD10组大鼠痛阈均较单纯致痛组显著升高,PD1组与PD10组痛阈升高差异无显著性.单纯致痛组DRG中谷氨酸转运体1(GLT-1)和兴奋性氨基酸载体1(EAAC1)表达显著高于对照组、PD1组、PD10组.除PD1组DRG中GLT-1表达高于对照组外,PD1组、PD10组及对照组DRG中GLT-1与EAAC1表达差异无显著性.结论:鞘内给予PD98059可减轻大鼠足底注射CFA引起的疼痛反应并减低致痛侧DRG中谷氨酸转运蛋白表达.     

全反式维甲酸联合猪胆酸钠对K562和Kasumi-1细胞系生物活性抑制作用

本研究旨在探索全反式维甲酸(all-trans retinoic acid,ATRA)联合猪胆酸钠(SBA-Na)对人白血病K562细胞系及Kasumi-1细胞系生物学活性的影响及其作用机制。分别配制浓度为10-6mol/L(W1)、10-4mol/L(W2)的ATRA溶液及浓度为100μg/ml(Z1)、200μg/ml(Z2)的SBA-Na溶液,分别使用W1、W2、Z1、Z2、W1+Z1、W2+Z2处理上述2种细胞系,并设立不加药的空白对照组。镜下观察不同处理组细胞形态及生长情况;应用CCK-8法检测细胞增殖能力,绘制细胞生长抑制曲线;分别采用PI单染和PI/Annexin V双染流式细胞术检测各加药组K562细胞和Kasumi-1细胞的细胞周期及凋亡的变化;采用实时荧光定量PCR(RQ-PCR)法检测K562细胞系各组CyclinA基因表达量的变化。结果表明,ATRA及SBA-Na对2种细胞均有抑制增殖作用,两者联合用药的作用更明显;各给药组与对照组相比,细胞周期分布发生明显变化,处理组细胞凋亡明显增加,尤以ATRA联合SBA-Na给药组凋亡最为明显。低浓度SBA-Na处理组Cyclin A表达上调,其他处理组Cyclin A表达均下调,且存在量效关系。结论:ATRA及SBA-Na均可抑制K562细胞及Kasumi-1胞系增殖,促进其凋亡,且二者联合效果更明显,对于K562细胞系,两者可能是通过下调Cyclin A基因表达而发挥作用。     

HL-60细胞的粒细胞分化中蛋白磷酸酯酶2Aa

蛋白磷酸酯酶按其底物分成丝氨酸/苏氨酸蛋白磷酸酯酶(PPs)和磷酸酪氨酸磷酸酯酶(PTPs)两类。根据对抑制剂1和2热稳定蛋白的敏感性,PPs又分为1PP型(PP-1)和2PP型(PP-2)。PP-1的活性受抑制剂1和2的抑制,而PP-2则对抗上述两种抑制剂。按对两价阳离子的依赖性,PP-2可再分成PP-2A,PP-2B和PP-2C 3型。近期的研究报道。PP-1和PP-2A与细胞周期和细胞增殖有关。在裂殖发     

有机阴离子转运多肽OATP1A2介导芬太尼的转运

目的:建立稳定表达有机阴离子转运多肽1A2(organic anion-transporting polypeptide 1A2,OATP1A2)的HEK293细胞株,体外研究OATP1A2是否转运芬太尼(Fentanyl)。方法:用脂质体转染法将pIRES2-Zs Green1-OATP1A2质粒转染至HEK293细胞中,G418(600 mg/ml)筛选单克隆阳性细胞,采用Western blot、RT-PCR证实HEK293-OATP1A2构建成功;用不同浓度的探针药物非索非那定(Fexofenadine,FEX)验证HEK293-OATP1A2的转运功能;运用不同浓度的芬太尼孵育细胞,另取两组用相同浓度的芬太尼孵育的细胞,分别加或不加抑制剂柚皮素(Naringenin,100μg/m L)进行HEK293-OATP1A2转运实验。结果:FEX浓度为1、10、100 nM时HEK293-OATP1A2实验组与HEK293-VC对照组,FEX的吸收值均有显著的统计学差异(P<0.05),且FEX浓度为100 nM时,实验组对FEX的吸收值是对照组的2.8倍;加入抑制剂柚皮素组FEX吸收值较不加抑制剂时减少了66.8±0.6%。芬太尼转运结果显示,芬太尼浓度为1、10、100、1000 nM时实验组与对照组比较,芬太尼的吸收值均有显著的统计学差异(P<0.05),且芬太尼浓度为1000 nM时,实验组对芬太尼的吸收值是对照组的2.2倍;加入抑制剂组芬太尼的吸收值较未加抑制剂组减少了86.5±0.5%(P<0.05)。结论:成功建立了稳定表达OATP1A2的HEK293细胞株,体外研究发现OATP1A2能介导芬太尼的转运。     

电击伤呼吸心跳停止30分钟抢救成功1例

活性的Mek。图2C示热休克不能激活白血病细胞的Raf-1, 而经热休克或用C2-鞘磷脂处理后的NIH3T3细胞中的Raf-1能被激活。2.3 D-MAPP对ERK活性的的影响加热（42℃，30min）前用碱性神经酰胺酶的抑制剂D-MAPP ](1S, 2R)-D-erythro-2 (N-Myristolamino)-1-phenyl-1-propanol, 5 mmol/L, 8h 或24h] 处理了NIH3T3细胞, 然后进行免疫复合物分析。结果显示用D-MAPP处理24h后，热休克引起的ERK活性下降了55%（图3）。2.4 热诱导ERK的磷酸化与Ras依赖途径为排除ERK的激活是通过热诱导的Ras依赖的途径，用稳定表达显性失活突变体Ra…     

Ethanol inhibition of constitutively open N-methyl-D-aspartate receptors

N-Methyl-D-aspartate (NMDA) receptors gate a slow and calcium-rich component of the postsynaptic glutamate response. Like all ionotropic glutamate receptors, NMDA subunits contain a highly conserved motif (SYTANLAAF) in the transmembrane (TM) 3 domain that is critically involved in channel gating. Mutation of an alanine in this domain (A7; underlined above) results in constitutively open receptors that show reduced sensitivity to several allosteric modulators. In this study, we examined the effects of ethanol, a substance that inhibits NMDA currents via an unknown mechanism, on tonically active NMDA receptors expressed in human embryonic kidney 293 cells. Ethanol (100 mM) inhibited currents from GluN1(A7R)/GluN2A and GluN1(A7R)/GluN2B receptors by approximately 50%, whereas those from GluN1/GluN2B(A7R) receptors were reduced by less than 10%. In cysteine-substituted GluN1 and GluN2 A7 mutants, estimated ethanol IC?? values for agonist-gated currents were 101, 117, 103, and 69 mM for GluN1(A7C)/GluN2A, GluN1(A7C)/GluN2B, GluN1/GluN2A(A7C), and GluN1/GluN2B(A7C) receptors, respectively. After exposure to the thiol-modifying reagent 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET), A7C mutants showed robust agonist-independent currents and reduced sensitivity to ethanol (IC?? values of 371, 256, 715, and 958 mM, respectively, as above). In contrast, cysteine modification of the ligand-binding domain resulted in constitutively open receptors that showed robust ethanol inhibition. Ethanol inhibition of MTSET-treated GluN1(A7C) receptors was further reduced by TM3/TM4 mutations previously shown to reduce ethanol sensitivity of agonist-gated receptors. Overall, these results show that ethanol affects NMDA receptor function at a site distal from agonist binding and appears to exert greater effects via perturbation of GluN2 subunits.     

In vivo analysis of the role of aberrant histone deacetylase recruitment and RAR alpha blockade in the pathogenesis of acute promyelocytic leukemia

The promyelocytic leukemia-retinoic acid receptor alpha (PML-RARalpha) protein of acute promyelocytic leukemia (APL) is oncogenic in vivo. It has been hypothesized that the ability of PML-RARalpha to inhibit RARalpha function through PML-dependent aberrant recruitment of histone deacetylases (HDACs) and chromatin remodeling is the key initiating event for leukemogenesis. To elucidate the role of HDAC in this process, we have generated HDAC1-RARalpha fusion proteins and tested their activity and oncogenicity in vitro and in vivo in transgenic mice (TM). In parallel, we studied the in vivo leukemogenic potential of dominant negative (DN) and truncated RARalpha mutants, as well as that of PML-RARalpha mutants that are insensitive to retinoic acid. Surprisingly, although HDAC1-RARalpha did act as a bona fide DN RARalpha mutant in cellular in vitro and in cell culture, this fusion protein, as well as other DN RARalpha mutants, did not cause a block in myeloid differentiation in vivo in TM and were not leukemogenic. Comparative analysis of these TM and of TM/PML(-/-) and p53(-/-) compound mutants lends support to a model by which the RARalpha and PML blockade is necessary, but not sufficient, for leukemogenesis and the PML domain of the fusion protein provides unique functions that are required for leukemia initiation.     

Testicular microlithiasis: our experience of 10 years.

OBJECTIVE: Testicular microlithiasis (TM) is characterized on sonography by multiple microprecipitates in the testes. The correlation between TM and testicular malignancies is variable. The purpose of this study was to review our 10-year experience regarding the prevalence of TM and its association with testicular malignancies. METHODS: This was a retrospective study in which 3254 testicular sonographic examinations over a 10-year period identified 137 patients with TM. Testicular microlithiasis was divided into 2 groups: classic TM (CTM; >or= 5 calcifications per image) and limited TM (<5 calcifications/image). A control population without TM was also randomly selected during the same period. Associations with testicular cancers and other findings were then noted and compared between the TM and control groups. RESULTS: One hundred thirty-seven (4.6%) of the 2957 individual patients with scrotal sonographic examinations had TM; 8 (5.8%) of the 137 patients with TM had testicular cancer, whereas 1 (0.73%) of the 137 patients without TM had primary testicular cancer (P = .04). There were 9 testicular neoplasms in 8 patients, all of whom had CTM. Thirty patients with TM and no malignancy were followed for an average of 19 months (range, 1-90 months; SD, 19.7 months); none had tumor development. CONCLUSIONS: We found a strong association between TM and testicular malignancy. We think that the most prudent use of resources for early detection of malignancy would be to have all patients with CTM perform testicular self-examinations, and follow-up sonography should be limited to a subgroup of patients with CTM and other associated risk factors.     

The putative transmembrane segment 7 of human organic anion transporter hOAT1 dictates transporter substrate binding and stability

Human organic anion transporter hOAT1 plays a critical role in the body disposition of clinically important drugs. We examined the role of the putative transmembrane segment (TM) 7 in the function of hOAT1. Each residue within putative TM7 was replaced by alanine, and the uptake of para-aminohippurate was studied in cells expressing the mutants. We discovered four critical amino acid residues: Trp-346, Thr-349, Tyr-353, and Tyr-354. Substitution of Tyr-353 and Tyr-354 with alanine led to the loss of transport activity without affecting the surface expression of the transporter, whereas substitution of Trp-346 and Thr-349 with alanine lead to the loss of the total expression of the transporter. The effect of side chains of Tyr-353 and Tyr-354 on transporter functions were further evaluated by replacing these residues with Phe or Trp. Among all the mutants studied (Y353W, Y353F, Y354W, and Y354F), only mutant Y353F regained 30% transport activity, which was lost from replacement of Tyr-353 with alanine, suggesting that both the -OH group and the size of the side chain at positions 353 and 354 are critical for maintaining the full transport activity. To investigate the mechanisms underlying the loss of total protein expression when Trp-346 and Thr-349 were replaced with alanine, mutant-expressing cells were treated with lysosomal or proteasomal inhibitors. Our results showed that only proteasomal inhibitors resulted in the accumulation of mutant proteins, indicating that proteasome is involved in the degradation of the mutant transporters. Therefore, Trp-346 and Thr-349 are critically involved in the stability of the transporter.     

Thrombomodulin modulates growth of tumor cells independent of its anticoagulant activity.

Thrombomodulin (TM), recognized as an essential vessel wall cofactor of the antithrombotic mechanism, is also expressed by a wide range of tumor cells. Tumor cell lines subcloned from four patients with malignant melanoma displayed a negative correlation between TM expression and cell proliferation in vitro and in vivo. Overexpression of wild-type TM decreased cell proliferation in vitro and tumor growth in vivo. TM mutants with altered protein C activation capacity lead to a similar effect. In contrast, transfection of melanoma cells with mutant TM constructs, in which a portion of the cytoplasmic or lectin domain was deleted, abrogated the antiproliferative effect associated with overexpression of wild-type TM. Experiments performed with either peptide agonists/antagonists of the thrombin receptor, with hirudin, or with inhibitors of thrombin-TM interaction did not alter the growth inhibitory effect of TM overexpression. These data suggest that TM exerts an effect on cell proliferation independent of thrombin and the thrombin receptor, possibly related to the binding of novel ligands to determinants in the lectin domain which might trigger signal transduction pathways dependent on the cytoplasmic domain.     

Antagonist efficacy in MORS196L mutant is affected by the interaction between transmembrane domains of the opioid receptor

In a previous study, we demonstrated that antagonists such as naloxone or naltrexone acted as full agonists at the mu-opioid receptor (MOR)/delta-opioid receptor (DOR) chimeric receptor (mudelta2, where the DOR sequence from the first extracellular loop to the carboxyl terminus was spliced to the MOR sequence) when a conserved serine residue in transmembrane 4 (TM4) was mutated to leucine. However, when Ser196 in the TM4 of MOR was mutated to Leu, antagonists exhibited partial agonistic properties. Since molecular modeling studies suggested transmembrane movement during receptor activation, the observed partial agonistic properties could be due to TM1 and TM7 interaction. Hence, MOR/DOR chimeric mutant receptors with the MOR TM1 and TM7 sequence (mudelta2mu7S196L) or with the MOR TM1 and TM6/7 sequence (mudelta2mu67S196L) were constructed to test such a hypothesis. Using four tests of opioid receptor activation, we found that the opioid antagonists were full agonists in chimeric mutant receptor if the TM1 and TM7 were from different opioid receptors. Additionally, when two of the TM7 amino acid residues of MORS196L receptor mutants were mutated (T327A and C330S), resulting in a mutant receptor with DOR TM7 sequence, opioid antagonist naloxone exhibited full agonistic properties. These data suggest that the efficacy of opioid antagonists in the Ser196 mutant can be affected by the interaction between TM1 and TM7.     

Treatment of Wilson's disease with zinc. XVIII. Initial treatment of the hepatic decompensation presentation with trientine and zinc

We have treated 9 patients who presented with hepatic decompensation resulting from Wilson's disease with a combination of trientine and zinc, generally for at least 4 months, followed by transition to zinc maintenance therapy. All of these patients had hypoalbuminemia, all but 1 had hyperbilirubinemia, and 7 had ascites. All of these patients would have been candidates for liver transplantation on the basis of their initial Child-Turcotte-Pugh (CTP) scores. The minimal listing criteria for transplant candidates is a score greater than 7. Eight of the 9 patients had demonstrated a CTP score of 10 or higher. The other scoring system that has been used in Wilson's disease to determine need for transplantation is the prognostic index of Nazer, in which a score over 6 indicates that the patient is unlikely to survive without a transplant if treated with penicillamine. Two of our patients had Nazer scores higher than 6. With our medical therapy, all 9 of these patients have recovered normal liver function as reflected by normalization of their CTP scores to 5. Because of coexisting neurologic disease, 1 of our 9 patients was initiated on a neurologic protocol and by chance randomized to receive tetrathiomolybdate (TM) and zinc after 2 weeks of trientine/zinc treatment. This patient's liver function recovered much more rapidly than did that of the other 8 patients, all of whom were treated with trientine/zinc, suggesting that TM therapy offers a further advantage. In summary, we were able to take 9 patients who presented with liver failure -8 of whom had CTP scores indicating a potential need for liver transplantation and 2 of whom had Nazer prognostic scores indicating that they were not likely to survive if treated only with penicillamine - and treat them medically, with recovery in all 9. We believe the trientine/zinc combination therapy should be the standard for initial treatment of liver failure in Wilson's disease because its efficacy is equal or slightly superior to that of penicillamine and because it has a much lower incidence of side effects. Moreover, TM warrants study to determine whether therapy for hepatic Wilson's disease can be further improved.     

Two amino acids in the sixth transmembrane segment of the mouse gastrin-releasing peptide receptor are important for receptor activation

The gastrin-releasing peptide receptor (GRP-R) is a G protein-coupled receptor that mediates a variety of cellular responses, including cell growth and modulation of neuronal activity by activation of heterotrimeric GTP-binding proteins in the Gq family. To understand the regulation of GRP-R signaling we have substituted alanine for each of 10 amino acid residues within the transmembrane (TM) helices of the GRP-R predicted to project into the binding pocket of the receptor and analyzed the importance of each of these residues for receptor function. Two mutations showed selective loss of either agonist (Y285A) or antagonist (F313A) affinity for the GRP-R. In addition, we identified two amino acid residues, Phe(270) and Asn(281), in the sixth TM segment, which are important for receptor-G protein interaction. In a competition-binding assay with an antagonist radioligand, bombesin showed a 20- to 100-fold decreased affinity for the N281A and F270A mutant GRP-R compared with wild-type GRP-R. The saturation-binding isotherms are best fit by a two-state model, indicating that the receptors are in either a low-affinity (K(D2)) or a high-affinity (K(D1)) state. The ratio of the two affinities (K(D2)/K(D1)) was significantly increased for both mutants compared with wild-type GRP-R, whereas the fraction of mutant receptors in the high-affinity state (R(1)) was decreased. GDP/guanosine-5'-O-(3-thio)triphosphate exchange catalyzed by the N281A mutant was lower than that observed for the wild-type GRP-R. However, for both mutants, bombesin was still able to stimulate 1,4,5-inositol triphosphate in transfected cells albeit with reduced activity. We conclude that these two TM residues are important for receptor-G protein coupling, and postulate that each mutation may affect GRP-R conformational change to the high-affinity, G protein-coupled state.     

A highly conserved aspartic acid (Asp-155) anchors the terminal amine moiety of tryptamines and is involved in membrane targeting of the 5-HT(2A) serotonin receptor but does not participate in activation via a "salt-bridge disruption" mechanism

Discovering the molecular and atomic mechanism(s) by which G-protein-coupled receptors (GPCRs) are activated by agonists remains an elusive goal. Recently, studies examining two representative GPCRs (rhodopsin and alpha(1b)-adrenergic receptors) have suggested that the disruption of a putative "salt-bridge" between highly conserved residues in transmembrane (TM) helix III, involving aspartate or glutamate, and helix VII, involving a basic residue, results in receptor activation. We have tested whether this is a general mechanism for GPCR activation by constructing a model of the 5-hydroxytryptamine (5-HT)(2A) receptor and characterizing several mutations at the homologous residues (Asp-155 and Asn-363) of the 5-HT(2A) serotonin receptor. All of the mutants (D155A, D155N, D155E, D155Q, and S363A) resulted in receptors with reduced basal activity; in no case was evidence for constitutive activity revealed. Structure-function studies with tryptamine analogs and various Asp-155 mutants demonstrated that Asp-155 interacts with the terminal, and not indole, amine moiety of 5-HT(2A) agonists. Interestingly, the D155E mutation interfered with the membrane targeting of the 5-HT(2A) receptor, and an inverse relationship was discovered when comparing receptor activation and targeting for a series of Asp-155 mutants. This represents the first known instance in which a charged residue located in a putative TM helix alters the membrane targeting of a GPCR. Thus, for 5-HT(2A) receptors, the TMIII aspartic acid (Asp-155) is involved in anchoring the terminal amine moiety of indole agonists and in membrane targeting and not in receptor activation by salt-bridge disruption.