重组人可溶性血管内皮细胞

血管内皮细胞生长抑制因子（Vascular Endothelial GrowthInhibitor,VEGI）是从人脐静脉内皮细胞（HUVEC）cDNA文库筛选到的一个TNF超家族新成员。为研究重组可溶性人VEGI对新生血管形成抑制活性,检测了重组可溶性人VEGI对建株人脐静脉内皮细胞（ECV304）增殖抑制活性以及对兔角膜诱生血管、鸡胚尿囊膜（CAM）血管的抑制活性。表明可溶性人VEGI可以直接抑制ECV304内皮细胞的增殖,抑制兔角膜诱生血管、CAM血管形成。VEGI是一种新的血管内皮细胞生长抑制因子,强烈抑制新生血管形成,有望应用于肿瘤的治疗。     

Envision法免疫组织化学染色研究重组人可溶性血管内皮细胞生长抑制因子的抗肿瘤活性

目的：研究重组人可溶性血管内皮细胞生长抑制因子(vascular endothelial growth inhibitor，VEGI)的抗肿瘤活性及其机制。方法：用重组人可溶性VEGI治疗荷S180肉瘤小鼠；第VIII因子相关抗原(FVIII RAg)标记肿瘤血管内皮细胞，用免疫组化Envision法检测瘤内微血管密度。结果：重组人可溶性VEGI显抑制S180肉瘤生长，肿瘤微血管密度大大减低。结论：VEGI具有较强的抗肿瘤活性，其机制可能是通过抗新生血管形成介导的。     

来源于Rhodotorula gracilis的D-氨基酸氧化酶的223、238位酪氨酸在催化中的作用：对双突变的阐释

黄素蛋白氧化酶的活性位点通常含有两个酪氨酸，例如Rhodotorula gracilis D-氨基酸氧化酶（DAAO）的Y223和Y238。这两个残基曾分别突变为苯丙氨酸和丝氨酸，为进一步研究其在酶催化中的作用，研究了Y223F—Y238F双突变。双突变的光谱性质与野生型的DAAO相似，预示着活性位点只发生了很少的变化，但催化活性有所降低。首先山乎预料的是双突变的很多性质比相应的单突变更相近于野生掣的DAAO，如更相似的动力学机理、底物特异性和氧化．还原性质。Y223F—Y238F双突变的DAAO与竞争性抑制剂的羧基结合能力略有下降（协同效应），     

第208位异亮氨酸对人细胞色素P4502A6尼古丁代谢活性的影响

目的探讨人体尼古丁主要代谢酶细胞色素P450(CYP)2A6及其同族成员CYP2A13肽链结构中,影响其尼古丁5′-羟化代谢活性的关键性氨基酸残基。方法使用前期制备的CYP2A6和CYP2A13系列氨基酸互换突变体:CYP2A6V117A,CYP2A6G164H,CYP2A6I208S,CYP2A6R372H和CYP2A6S465P以及CYP2A13A117V,CYP2A13H164G,CYP2A13S208I,CYP2A13H372R和CYP2A13P465S,比较其与相应野生蛋白酶的尼古丁5′-羟化催化反应的动力学参数。结果各突变体对2个CYP2A蛋白酶的尼古丁代谢活性影响不同。对于CYP2A6,I208S突变对酶活性的影响显著,导致表观反应常数Km及最大反应速度Vmax由野生型62.25μmol.L-1和6.53mol.min-1.mol-1变化为345μmol.L-1和2.19mol.min-1.mol-1,但该位点对CYP2A13酶活性无显著影响;对于CYP2A13,H372R突变对酶活性的影响最为显著,导致Km及Vmax由野生型的26.01μmol.L-1和24.51mol.min-1.mol-1变为148.7μmol.L-1和6.11mol.min-1.mol-1,此位点对CYP2A6无显著影响。其他位点突变对酶活性影响较小或不显著。结论CYP2A家族蛋白中,I208与H372分别是影响CYP2A6和CYP2A13对尼古丁代谢的关键残基。对于同家族蛋白酶而言,关键性氨基酸的作用并不总是一一对应。     

基因重组长效人促肾上腺皮质激素药理学活性

目的为了提高促肾上腺皮质激素(adrenocorticotropic hormone,ACTH)的稳定性,针对ACTH中多种血液蛋白酶的作用位点,制备特定氨基酸位点突变(E5D、F7L、G10A及Y2S)基因重组长效人ACTH,分析比较哪一种点突变基因重组ACTH保留了天然野生型的生理活性。方法采用ELISA和q PCR等方法比较了4种突变型ATCH与野生型ACTH对体外培养的小鼠肾上腺皮质Y1细胞分泌糖皮质激素(glucocorticoids,GC)水平的影响,以及它们对ACTH合成的主要限速酶基因(STAR、P450-scc、3β-HSD)以及对STAR和P450-scc的合成发挥关键调节作用的类固醇合成因子1(SF-1)的转录水平的影响。结果 E5D及Y2S突变型ACTH对Y1细胞分泌GC以及对SF-1、STAR、P450-scc、3β-HSD等基因表达的影响与野生型ACTH比较,没有显著性差异。结论一级结构修饰的E5D和Y2S突变型ACTH的生理活性与野生型ACTH相当。     

α7烟碱型乙酰胆碱受体点突变体的制备及其功能研究

目的 利用氨基酸定点突变技术以大鼠野生型α7烟碱型乙酰胆碱受体(nAChR)为模板制备α7 nAChR突变体。方法 采用体外转录、定点突变、凝胶电泳、双电极电压钳等技术对α7 nAChR进行点突变,在非洲爪蟾卵母细胞上表达α7 nAChR及其突变体,并研究其受体活性功能。结果 将α7 nAChR第111位的丙氨酸突变为丝氨酸,制备了α7 nAChR的点突变体,测定了突变体对激动剂乙酰胆碱(ACh)的半数效应浓度(EC₅₀)为165.6 μmol/L。结论 该结果不仅为受体定点突变提供了一种方法,同时为药物筛选和研究α7 nAChR结构与功能关系提供了模型。     

蝎镇痛抗肿瘤缬精甘肽的两个氨基酸残基对镇痛活性的影响

目的研究蝎镇痛抗肿瘤缬精甘肽(analgesic-antitumor peptide,AGAP)中2个氨基酸残基对其镇痛活性的影响。方法利用已构建成功的2个突变体W38G和R58D,采用金属离子螯合亲和层析和阳离子交换层析方法对突变体蛋白进行纯化。采用小鼠醋酸扭体法测定两个突变体的镇痛活性。结果在大肠杆菌BL21(DE3)中实现了可溶性表达。采用金属离子螯合层析和阳离子交换层析方法获得了电泳纯样品。突变体W38G镇痛活性与未突变重组蛋白(recombinant analgesic-antitumor peptide from Buthus martensii Karschr,BmK AGAP)相同,突变体R58D镇痛活性降低。结论突变体与rBmK AGAP相比镇痛活性发生变化,说明所选取的突变位点对蝎镇痛抗肿瘤缬精甘肽的镇痛活性具有一定的调节作用。     

血管内皮细胞非神经性乙酰胆碱系统的研究进展

血管内皮细胞作为人体主要的代谢库,存在ACh ,并伴有ChAT的表达,有机阳离子载体(OCTs)参与血管内皮细胞ACh的转运和释放,血管内皮细胞AChE活性的广泛表达可以使非神经性ACh的活性仅仅局限于它的合成和释放区域,成为一种细胞因子。mAChR和nAChR同非神经性ACh一样,广泛存在于血管内皮细胞中,ACh通过其受体发挥重要的病理生理功能。nAChR参与血管内皮细胞多种生物活性物质的分泌和释放,其中α7受体在血管新生中发挥重要作用。非神经性ACh诱发内皮依赖的血管舒张反应,一种不同于神经性mAChR的血管内皮细胞非神经性M受体在其中发挥重要作用,并且在动脉粥样硬化和血栓的发生发展过程中起着重要的作用。     

双作用靶点水蛭素Ⅲ突变体库(R33G34D35X36-rHV3)的构建及最适突变体筛选

构建水蛭素Ⅲ(HVⅢ)突变体库R33G34D35X36-rHVⅢ,从中筛选出具有与重组水蛭素Ⅲ(rHV3)抗凝血酶活性比活力相当,同时又具有很强的抗ADP诱导的血小板聚集抑制率的双作用靶点水蛭素Ⅲ突变体。通过基因定点突变技术构建水蛭素Ⅲ突变库R33G34D35X36-rHVⅢ,表达纯化后通过凝血酶滴定方法测定其抗凝血酶比活性,同时测定其抗ADP诱导的血小板聚集比活性。结果显示所有突变体的抗凝血酶比活性未发生变化,但各突变体抗ADP诱导的血小板聚集的比活性各异,当第36位为Met和Ser时所表现的抗ADP诱导的血小板聚集的比活性最强。由此可知水蛭素Ⅲ(HVⅢ)突变体库R33G34D35X36-rHVⅢ中第36位氨基酸种类对其抗凝血酶活性影响不大,但对其抗ADP诱导的血小板聚集的比活性影响较大,当该位点为Met和Ser时突变体具有很好的抗凝血酶和抗ADP诱导的血小板聚集的双重药理活性。     

转录因子SOXF家族调控内皮细胞的研究进展

目的 内皮细胞是血管发育、分化及损伤后修复的基础,内皮细胞的形成和发育进程受一系列基因、转录因子、信号通路等调控.转录因子SOXF家族(SRY related high mobility group box F)在调控内皮细胞生成、增殖及转化等进程中发挥重要作用.SOXF与众多参与调控血管内皮细胞的转录因子存在调节关系,但其调控内皮细胞的确切分子机制未来需进一步研究.     

Molecular mechanisms of constitutive activity: mutations at position 111 of the angiotensin AT1 receptor

Abstract: A possible molecular mechanism for the constitutive activity of mutants of the angiotensin type 1 receptor (AT₁) at position 111 was suggested by molecular modeling. This involves a cascade of conformational changes in spatial positions of side chains along transmembrane helix (TM3) from L112 to Y113 to F117, which in turn, results in conformational changes in TM4 (residues I152 and M155) leading to the movement of TM4 as a whole. The mechanism is consistent with the available data of site‐directed mutagenesis, as well as with correct predictions of constitutive activity of mutants L112F and L112C. It was also predicted that the double mutant N111G/L112A might possess basal constitutive activity comparable with that of the N111G mutant, whereas the double mutants N111G/Y113A, N111G/F117A, and N111G/I152A would have lower levels of basal activity. Experimental studies of the above double mutants showed significant constitutive activity of N111G/L112A and N111G/F117A. The basal activity of N111G/I152A was higher than expected, and that of N111G/Y113A was not determined due to poor expression of the mutant. The proposed mechanism of constitutive activity of the AT₁ receptor reveals a novel nonsimplistic view on the general problem of constitutive activity, and clearly demonstrates the inherent complexity of the process of G protein‐coupled receptor (GPCR) activation.     

Identification of key residues responsible for enzymatic and platelet-aggregation-inhibiting activities of acidic phospholipase A2S from Agkistrodon halys Pallas

Site-directed mutagenesis was used to probe the structural and functional relationship of acidic phospholipase A2 from Agkistrodon halys Pallas. The mutants are AP-E6R (E6R), AP-D115K (D115K), AP-6R115K (E6R, D115K), AP-Y118M (Y118M), and AP-W119T (W119T). All mutants were inserted into a bacterial expression vector and effectively expressed in E. coli RR1. The purified recombinant enzymes were used to assay for enzymatic and inhibiting platelet aggregation activities. The enzymatic activities of AP-D115K, AP-Y118M and AP-W119T are close to that of denatured-refolded acidic phospholipase A2, while the enzymatic activities of AP-E6R, AP-6R1 15K are lower than that of denatured-refolded acidic phospholipase A2 (AP-WT). In these five mutants, AP-Y118M showed strongest inhibiting effect on platelet aggregation, which is the same as that of AP-WT, AP-W119T showed only modest activity and AP-E6R, AP-D115K, AP-6R115K showed little activity. To study the structural and functional relationships among these five mutants, molecular modeling of these five mutants was done. The roles of various amino acid residues in the enzymatic activity and pharmacological activity of acidic phospholipase A2 are discussed.     

A different molecular interaction of bradykinin and the synthetic agonist FR190997 with the human B2 receptor: evidence from mutational analysis

Binding affinity at the [3H]-BK binding site and activity as inositol phosphate (IP) production by the peptide bradykinin (BK) and the nonpeptide FR190997 were studied at wild-type or point-mutated human B2 receptors (hB2R) expressed in CHO cells. The effect of the following mutations were analyzed: E47A (TM1), W86A and T89A (TM2), I110A, L114A and S117A (TM3), T158A, M165T and L166F (TM4), T197A and S211A (TM5), F252A, W256A and F259A (TM6), S291A, F292A, Y295A and Y295F (TM7), and the double mutation W256A/Y295F. As the wild-type receptor-binding affinity of FR190997 was 40-fold lower than BK, whereas their agonist potency was comparable, both agonists produced similar maximal effects (Emax). Mutations were evaluated as affecting the affinity and/or efficacy of FR190997 compared with BK. Two mutations were found to impair the agonist affinity of both agonists drastically: W86A and F259A. BK agonist affinity (pEC50) was reduced by 1400- and 150-fold, and that of FR190997 was reduced by 400- and 25-fold, at the W86A and F259A mutant B2 receptors, respectively. Contrary to BK, the affinity of FR190997 was selectively decreased at I110A, Y295A, and Y295F mutants (>103-fold), and a different efficacy was measured at the Y295 mutants, FR190997 being devoid of the capability to trigger IP production at Y295A mutant. L114A, F252A, and W256A selectively impaired the efficacy of FR190997, whereas its binding affinity was not affected. As a consequence, FR190997 behaved as a high-affinity antagonist in blocking the IP production induced by BK. The lack of capability of FR190997 to activate or to bind the double mutant W256A/Y295F suggests that these residues are part of the same binding site, which is also important for receptor activation by the nonpeptide ligand. Overall, by means of mutational analysis, we indicate an hB2R recognition site for the nonpeptide agonist FR190997 (between TM3, 6, and 7), different from that of BK, and show that in the same binding crevice some mutations (L114, W256, and F252) are selectively responsible for the agonist properties of only FR190997.     

How batrachotoxin modifies the sodium channel permeation pathway: computer modeling and site-directed mutagenesis

A structural model of the rNav1.4 Na+ channel with batrachotoxin (BTX) bound within the inner cavity suggested that the BTX pyrrole moiety is located between a lysine residue at the DEKA selectivity filter (Lys1237) and an adjacent phenylalanine residue (Phe1236). We tested this pyrrole-binding model by site-directed mutagenesis of Phe1236 at D3/P-loop with 11 amino acids. Mutants F1236D and F1236E expressed poorly, whereas nine other mutants either expressed robust Na+ currents, like the wild-type (F1236Y/Q/K), or somewhat reduced current (F1236G/A/C/N/W/R). Gating properties were altered modestly in most mutant channels, with F1236G displaying the greatest shift in activation and steady-state fast inactivation (-10.1 and -7.5 mV, respectively). Mutants F1236K and F1236R were severely resistant to BTX after 1000 repetitive pulses (+50 mV/20 ms at 2 Hz), whereas seven other mutants were sensitive but with reduced magnitudes compared with the wild type. It is noteworthy that rNav1.4-F1236K mutant Na+ channels remained highly sensitive to block by the local anesthetic bupivacaine, unlike several other BTX-resistant mutant channels. Our data thus support a model in which BTX, when bound within the inner cavity, interacts with the D3/P-loop directly. Such a direct interaction provides clues on how BTX alters the Na+ channel selectivity and conductance.     

Characterization of the biochemical and structural phenotypes of four CYP1B1 mutations observed in individuals with primary congenital glaucoma

OBJECTIVE: The objective of this study was to examine the biochemical and physical properties of cytochrome P450 1B1 (CYP1B1) mutants, test our hypothesis that primary congenital glaucoma (PCG)-causing mutants have altered metabolic activity, and correlate these to structural changes in the molecule. METHODS: CYP1B1.1 cDNA was mutated to four forms found in individuals with the PCG phenotype, Y81N, E229K, A330F, and R368H. Expression and stability of the mutant hemoproteins and their ability to metabolize beta-estradiol, arachidonic acid, and retinoids, were determined. Alterations in mutant properties were related to structural changes by in silico examination, on the basis of the CYP1A2 crystal structure. RESULTS: CYP1B1 mutations strongly affected the stability, ease of heterologous expression, and enzymatic properties of the protein. These were related to the location of the amino acid substitutions in the CYP1B1 structure. Three of the mutations involve residues located on the surface of CYP1B1, Y81N, and E229K near the distal surface, and R368H near the proximal surface. The former two substitutions, Y81N and E229K, caused greatly reduced stability at 4 degrees C. Y81N severely inhibited all substrate turnover, but E229K only inhibited arachidonate turnover and exhibited minimal effect on efficiency of retinoid metabolism and estradiol metabolism. The R368H mutation is relatively conservative, affecting charge-pairing with the deeper-located D374, but it severely inhibited metabolism of all substrates tested, and, like Y81N, expression of the enzyme is less facile than CYP1B1wt. The A330F mutation replaces a small alanine by a bulky phenylalanine in the enzyme active site and had major impact on substrate binding, turnover, uncoupling, and metabolite pattern. CONCLUSION: Consistent with the hypothesis, these PCG-related mutations cause identifiable structural changes negatively impacting CYP1B1 biochemistry and stability.     

Random mutagenesis of the human adenosine A2B receptor followed by growth selection in yeast. Identification of constitutively active and gain of function mutations

To gain insight in spontaneous as well as agonist-induced activation of the human adenosine A2B receptor, we applied a random mutagenesis approach in yeast to create a large number of receptor mutants and selected mutants of interest with a robust screening assay based on growth. The amino acid sequence of 14 mutated receptors was determined. All these mutated receptors displayed constitutive activity. In particular, single-point mutations at T42A, V54L, and F84S and a triple-point mutation at N36S, T42A, and T66A resulted in high constitutive activity. In addition, a C-terminally truncated (after Lys269) mutant, Q214L I230N V240M V250M N254Y T257S K269stop, was highly constitutively active. The T42A, V54L, and F84S mutants showed a considerable decrease, 4.9- to 6.9-fold, in the EC50 value of 5'-N-ethylcarboxamidoadenosine (NECA), an adenosine analog. Combined mutation of I242T, K269R, V284A, and H302Q, as well as F84L together with S95G, resulted in an even greater potency of NECA of 10- and 18-fold, respectively. In fact, all constitutively active mutants had an increased potency for NECA. This suggests that the wild-type (wt) human A2B receptor itself is rather silent, which may explain the low affinity of agonists for this receptor. To verify the ability of the mutant receptors to activate mammalian second messenger systems, cAMP experiments were performed in CHO cells stably expressing the wt and T42A receptors. These experiments confirmed the increased sensitivity of T42A for NECA, because the EC50 values of T42A and the wt receptor were 0.15 +/- 0.04 and 1.3 +/- 0.4 microM, respectively.     

None of the four tyrosine residues is essential for the biological activity of erythropoietin

Erythropoietin (EPO), a glycoprotein hormone, regulates the proliferation and differentiation of erythroid progenitor cells. Many attempts have been made to identify the functionally important amino acids of the hormone. One of those early studies has found that heavy radioiodination of EPO caused the loss of its biological activity, suggesting some important role of one of the four tyrosine residues (Goldwasser, 1981). Thus, in this study, we have generated and tested four Tyr→Phe substitution mutants to clarify the possible role of the tyrosine residue(s) in the hormone’s biological activity. When the mutant and wild type EPO cDNAs were transfected into COS-7 cells and the biological activities of the muteins were assayed using the primary murine erythroid spleen cells, no mutation tested was found to affect the biological activity of the hormone. Thus we conclude that, contrary to the previous observation, none of the four tyrosine residues in erythropoietin is critically involved in the binding of the hormone to its receptor.     

Key amino acid residues responsible for the differences in substrate specificity of human UDP-glucuronosyltransferase (UGT)1A9 and UGT1A8

Human UDP-glucuronosyltransferase (UGT)1A9 is one of the major isoforms in liver and extrahepatic tissues, catalyzing the glucuronidation of a variety of drugs, dietary constituents, steroids, fatty acids, and bile acids. UGT1A9 shows high amino acid homology with UGT1A7, UGT1A8, and UGT1A10 with overlapping substrate specificity. However, the affinities for substrates are different among them. Amino acid alignment analysis revealed that 14 amino acids, Cys3, Arg42, Lys91, Ala92, Tyr106, Gly111, Tyr113, Asp115, Asn152, Leu173, Leu219, His221, Arg222, and Glu241, are unique to UGT1A9 compared with UGT1A7, UGT1A8, and UGT1A10. In this study, we constructed expression systems in human embryonic kidney 293 cells for seven mutants (Mut) UGT1A9, Mut 1 (R42Q), Mut 2 (K91M, A92D), Mut 3 (Y106F, G111S, D115G), Mut 4 (N152A), Mut 5 (L173A), Mut 6 (L219F, H221Q, R222Y), and Mut 7 (E241A), in which the amino acids were substituted to those of UGT1A8. Using these mutants, the effects of the amino acid changes on the activities of 4-methylumbelliferone (4-MU), p-nitrophenol (p-NP), and 3-hydroxydesloratadine glucuronidations were investigated. For 4-MU and p-NP O-glucuronidations, Mut 1 and Mut 4 exhibited higher K(m) values and Mut 3 and Mut 4 exhibited higher V(max) values compared with wild-type UGT1A9. It is interesting to note that only Mut 4 was active toward 3-hydroxydesloratadine O-glucuronidation that is specific for UGT1A8. The findings reveal that the residues Arg42 and Asn152 may have a large contribution to the difference in the substrate specificity with that of UGT1A8, although all of the unique amino acids of UGT1A9 would be collectively involved in the catalytic property.     

Point mutations in either subunit of the GABAB receptor confer constitutive activity to the heterodimer

The GABA receptor (GABABR) is a class C G protein-coupled receptor (GPCR) that functions as an obligate heterodimer, composed of two heptahelical subunits, GABABR subunit 1 (R1) and GABABR subunit 2 (R2). In this study, we generated and pharmacologically characterized constitutively active GABABR mutants as novel tools to explore the molecular mechanisms underlying receptor function. A single amino acid substitution, T290K, in the R1 agonist binding domain results in ligand-independent signaling when this mutant subunit is coexpressed with wild-type R2. Introduction of a Y690V mutation in the putative G protein-coupling domain of R2 is sufficient to confer moderate constitutive activity when this subunit is expressed alone. Activity of the Y690V mutant can be markedly enhanced with coexpression of wild-type R1. Coexpression of both mutant subunits (R1-T290K and R2-Y690K) leads to a further increase in basal signaling. Potencies of the full agonists R-(+)-beta-(aminomethyl)-4-chlorobenzenepropanoic acid hydrochloride (baclofen) and GABA are increased at the constitutively active versus the corresponding wild-type receptors. The mutant GABABR variants provided a sensitive probe enabling detection of inverse or partial agonist activity of molecules previously considered neutral antagonists. Our studies using constitutively active isoforms provide independent support for a model of GABABR function that takes into account 1) ligand binding by R1, 2) signal transduction by R2, and 3) modulation of R2-induced function by R1. Furthermore, we demonstrate that certain hallmark features of constitutive activity as originally established with class A GPCRs (e.g., enhanced agonist potency and affinity), are more generally applicable, as suggested by our finding with a class C heterodimeric receptor.