共查询到20条相似文献，搜索用时 15 毫秒
1.
L W Hardy J S Finer-Moore W R Montfort M O Jones D V Santi R M Stroud 《Science (New York, N.Y.)》1987,235(4787):448-455
The atomic structure of thymidylate synthase from Lactobacillus casei was determined at 3 angstrom resolution. The native enzyme is a dimer of identical subunits. The dimer interface is formed by an unusual association between five-stranded beta sheets present in each monomer. Comparison of known sequences with the Lactobacillus casei structure suggests that they all have a common core structure around which loops are inserted or deleted in different sequences. Residues from both subunits contribute to each active site. Two arginine side chains can contribute to binding phosphate on the substrate. The side chains of several conserved amino acids can account for other determinants of substrate binding. 相似文献
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Molecular modeling of the HIV-1 protease and its substrate binding site 总被引：13，自引：0，他引：13
I T Weber M Miller M Jaskólski J Leis A M Skalka A Wlodawer 《Science (New York, N.Y.)》1989,243(4893):928-931
The human immunodeficiency virus (HIV-1) encodes a protease that is essential for viral replication and is a member of the aspartic protease family. The recently determined three-dimensional structure of the related protease from Rous sarcoma virus has been used to model the smaller HIV-1 dimer. The active site has been analyzed by comparison to the structure of the aspartic protease, rhizopuspepsin, complexed with a peptide inhibitor. The HIV-1 protease is predicted to interact with seven residues of the protein substrate. This information can be used to design protease inhibitors and possible antiviral drugs. 相似文献
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Domain separation in the activation of glycogen phosphorylase a 总被引：3，自引：0，他引：3
E J Goldsmith S R Sprang R Hamlin N H Xuong R J Fletterick 《Science (New York, N.Y.)》1989,245(4917):528-532
The crystal structure of glycogen phosphorylase a complexed with its substrates, orthophosphate and maltopentaose, has been determined and refined at a resolution of 2.8 angstroms. With oligosaccaride bound at the glycogen storage site, the phosphate ion binds at the catalytic site and causes the regulatory and catalytic domains to separate with the loss of stabilizing interactions between them. Homotropic cooperativity between the active sites of the allosteric dimer results from rearrangements in isologous contacts between symmetry-related helices in the subunit interface. The conformational changes in the core of the interface are correlated with those observed on covalent activation by phosphorylation at Ser14 (phosphorylase b----a). 相似文献
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[目的]确定猴头菇氨基酸营养液的最佳制备工艺,为以猴头菇为原料的氨基酸强化食品开发提供参考.[方法]以猴头菇营养液中的氨基酸总量为指标,采用单因素试验和正交试验对影响氨基酸总量的酸性蛋白酶用量、纤维素酶用量、酶解温度、酶解时间、酶解pH、液料比等因素进行优化.[结果]影响猴头菇营养液中氨基酸总量的主次因素依次为:酸性蛋白酶用量>纤维素酶用量>液料比>酶解时间>酶解温度>酶解pH,其最佳制备工艺参数为:酸性蛋白酶用量1.00%,纤维素酶用量1.50%,酶解温度50℃,酶解时间60 min,酶解pH 3.5,液料比25∶1.与热水浸提法相比,双酶法制备的猴头菇氨基酸营养液中氨基酸总量提高了73.2%、可溶性固形物含量提高了75.0%.[结论]以双酶法制备猴头菇氨基酸营养液是可行的,能有效提高营养液中的氨基酸总量和可溶性固形物含量. 相似文献
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蛋白酶和植酸酶联合添加降低肉仔鸡氮磷排放的研究 总被引：1，自引：0，他引：1
探讨不同酶制剂组合在低能、低氮蛋白、低磷日粮中对肉仔鸡生产性能和氮、磷排放的影响。选用288只1日龄爱拔益加父母代母系公雏,进行4种日粮处理:①按总氨基酸需要配制正常能量、粗蛋白质和总磷营养水平日粮(CK正),②按可消化氨基酸需要配制低能、低蛋白、低磷日粮(CK低),以及在CK低基础上分别添加③蛋白酶+植酸酶和④蛋白酶+淀粉酶+木聚糖酶+植酸酶共2种组合的酶制剂,测定了生产性能、氮、磷代谢等指标。结果表明:低营养水平日粮(CK低)导致肉仔鸡生产性能显著下降,添加2种酶制剂组合均能显著改善其生产性能和综合生产指数,达到正常营养水平日粮(CK正)的效果。2种酶制剂组合均显著降低粪便中磷、氮排放,其中以蛋白酶+植酸酶组合效果最好,按食入日粮计磷、氮排放分别比CK正降低26.06%和10.76%。结果说明,蛋白酶+植酸酶组合更有利于提高氮、磷利用率进而降低肉仔鸡粪便氮、磷的排放。 相似文献
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Three-dimensional structure of favin: saccharide binding-cyclic permutation in leguminous lectins 总被引：4，自引：0，他引：4
The three-dimensional structure of favin, the glucose- and mannose-binding lectin of Vicia faba (vetch, broad bean), has been determined at a resolution of 2.8 angstroms by molecular replacement. The crystals contain specifically bound glucose and provide the first high-resolution view of specific saccharide binding in a leguminous lectin. The structure is similar to those of concanavalin A (Con A) and green pea lectin; differences from Con A show that minimal changes are needed to accommodate the cyclic permutation in amino acid sequence between the two molecules. The molecule is an ellipsoidal dimer dominated by extensive beta structures. Each protomer contains binding sites for two divalent metal ions (Mn2+ and Ca2+) and a specific saccharide. Glucose is bound by favin in a cleft in the molecular surface and has noncovalent contacts primarily with two peptide loops, one of which contains several metal ion ligands. The specific carbohydrate-binding site is similar to that of Con A in location and general peptide folding, despite several differences in specific amino acid residues. 相似文献
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[目的]明确卵形鲳鲹组织蛋白酶L基因(TroCatL)的遗传进化规律及其组织表达水平,为研究CatL生物学功能及其对病原的抗病机理提供理论依据.[方法]应用RT-PCR和RACE技术克隆TroCatL基因全长cDNA,采用生物信息学方法对其序列特征进行分析;并以实时荧光定量PCR(qPCR)检测TroCatL基因在健康组织中的表达情况及其表达与溶藻弧菌感染的关联性.[结果]TroCatL基因全长cDNA为1492 bp(GenBank登录号MH036350),包括开放阅读框(ORF)1011 bp、5'端非翻译区(5'-UTR)120 bp和3'端非翻译区(3'-UTR)361 bp. TroCatL基因编码336个氨基酸残基,其理论等电点(pI)5.7,预测分子质量37.93 kD,且存在CatL特有的保守结构域(ERFNIN、GNFD和GCXGG基序)及由139Cys、279His和303Asn组成的半胱氨酸蛋白酶保守活性位点.TroCatL氨基酸序列与其他鱼类CatL氨基酸序列的同源性高达83.9%~95.2%,尤其与鲈形目鰤鱼的亲缘关系最近. TroCatL基因mRNA在健康卵形鲳鲹组织中均有表达,以在肝脏中的表达最高,在脑组织中的表达最低.经溶藻弧菌感染后,TroCatL基因mRNA在肝脏、脾脏和血液中的表达水平均上调,肝脏和脾脏中的TroCatL基因mRNA在攻毒后24 h达峰值,血液中的TroCatL基因mRNA在感染后12 h达最高值.[结论]TroCatL蛋白结构域及其催化活性位点在遗传进化过程中较保守,通过参与机体的免疫应答反应,在卵形鲳鲹抵御细菌或病毒侵染的过程中扮演重要角色. 相似文献
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通过室内模拟抗性汰选出抗三氟氯氰菊酯截形叶螨种群。利用蛋白酶 Ｋ 及十二烷基硫酸钠、乙二胺四乙酸钠盐等裂解叶螨细胞,提取基因组 Ｄ Ｎ Ａ。参照有关大鼠、果蝇钠通道的核酸序列,设计２５ 、２７ 个核甙酸的引物对,采用聚合酶链反应分别对抗三氟氯氰菊酯种群和敏感种群进行扩增,产物扩增片段为３００ｂｐ 。由扩增结果得知,引物设计合理,并可推测：截形叶螨对菊酯类农药产生强抗药性的原因并非是由于钠通道基因的突变作用引起 相似文献
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酶法制备大豆蛋白成骨活性肽 总被引：1，自引：0，他引：1
【目的】探究从大豆分离蛋白双酶分步酶解产物中分离促成骨细胞增殖肽的工艺,为大豆产品的开发提供参考。【方法】以促成骨细胞增殖活性作为测定指标,选用木瓜蛋白酶酶解大豆分离蛋白（SPI）,采用MTT法检测不同浓度的木瓜蛋白酶酶解产物对成骨细胞的促增殖活性。采用pH-Stat法检测水解时间为1、2、3、4、5和6 h的木瓜蛋白酶酶解产物的水解度,并检测相应水解时间的酶解产物对成骨细胞的促增殖活性。然后分别采用截留分子量为30 kD和10 kD两种超滤膜对活性较高的酶解产物进行超滤,并测定各超滤组分对成骨细胞的促增殖活性。再将具有较高促成骨细胞增殖活性的超滤组分分别在0.5、1、1.5、2和2.5 h进行碱性蛋白酶酶解,并检测相应水解时间的酶解产物对成骨细胞的促增殖活性。然后选用交联葡聚糖（Sephadex G-15）对具有较高促成骨细胞增殖活性的酶解产物进行分离,并检测各分离组分对成骨细胞的促增殖活性。最后,对各分离组分进行氨基酸分析,并采用质谱（ESI-TOF MS/MS）对最高促成骨细胞增殖活性的分离组分进行结构鉴定,并筛选出具有较强促成骨细胞增殖的大豆活性肽。【结果】在浓度为200 μg·mL -1时,木瓜蛋白酶酶解物对成骨细胞的促增殖活性随着酶解时间的增加逐渐增强,当酶解时间为5 h时达到最高促增殖活性（（118.24±2.73）%）。木瓜蛋白酶酶解产物经超滤分离、碱性蛋白酶酶解和凝胶过滤色谱分离后,对各分离组分进行氨基酸分析并筛选得到对成骨细胞具有最强增殖活性的组分F3,该组分的成骨细胞增殖率为（125.80±2.94）%,且F3中丙氨酸、缬氨酸、异亮氨酸、亮氨酸、苯丙氨酸等疏水性氨基酸以及芳香族氨基酸和必需氨基酸的含量明显高于其他组分。进一步通过质谱鉴定出F3主要由10个肽段组成。其中,DAMDGWFRL、GQTPLFPR、ADFYNPK、KDWYDIK的疏水性氨基酸、芳香族氨基酸以及必需氨基酸占比较高。对上述4个肽段进行活性测定,发现GQTPLFPR的促成骨细胞增殖活性最强,在浓度为100 μmol·L-1时,其成骨细胞增殖率为（129.11±3.12）%。【结论】采用双酶分步酶解结合超滤和凝胶过滤色谱等蛋白分离纯化技术,从大豆分离蛋白中分离纯化出了具有较强促成骨细胞增殖活性的多肽,为促成骨细胞增殖活性肽的制备和应用提供了技术参考。 相似文献
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Acetyl-coenzyme A carboxylases (ACCs) are required for the biosynthesis and oxidation of long-chain fatty acids. They are targets for therapeutics against obesity and diabetes, and several herbicides function by inhibiting their carboxyltransferase (CT) domain. We determined the crystal structure of the free enzyme and the coenzyme A complex of yeast CT at 2.7 angstrom resolution and found that it comprises two domains, both belonging to the crotonase/ClpP superfamily. The active site is at the interface of a dimer. Mutagenesis and kinetic studies reveal the functional roles of conserved residues here. The herbicides target the active site of CT, providing a lead for inhibitor development against human ACCs. 相似文献
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A thermodynamic scale for the helix-forming tendencies of the commonly occurring amino acids 总被引：76，自引：0，他引：76
Amino acids have distinct conformational preferences that influence the stabilities of protein secondary and tertiary structures. The relative thermodynamic stabilities of each of the 20 commonly occurring amino acids in the alpha-helical versus random coil states have been determined through the design of a peptide that forms a noncovalent alpha-helical dimer, which is in equilibrium with a randomly coiled monomeric state. The alpha helices in the dimer contain a single solvent-exposed site that is surrounded by small, neutral amino acid side chains. Each of the commonly occurring amino acids was substituted into this guest site, and the resulting equilibrium constants for the monomer-dimer equilibrium were determined to provide a list of free energy difference (delta delta G degree) values. 相似文献
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半胱氨酸蛋白酶是植物体中重要的蛋白水解酶,广泛参与种子萌发、幼苗发育、胁迫响应和组织分化衰老等生理过程.我们对水稻中半胱氨酸蛋白酶基因OsCF2 (Oryza sativa cysteine protease 2)序列进行分析.该基因cDNA全长2 279 bp,由2个外显子和1个内含子组成;包含1个1 089 bp的开放读码框,编码1个含362个氨基酸残基的蛋白,在蛋白氨基端有-36个氨基酸组成的信号肽.生物信息学分析表明,OsCP2与大麦半胱氨酸蛋白酶HvCP同源性最高,同属木瓜蛋白酶亚家族.另外,我们构建了pET32a/CP2原核.表达载体,通过转化大肠杆菌BL21DE3,成功表达了OsCP2重组蛋白.分子量约为58kD;通过纯化包涵体获得了纯度高达90%以上的重组OsCP2蛋白,这为进一步研究该基因的功能提供了基础. 相似文献
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以甘蔗花叶病毒(SCMV)福建分离物(FJ)的总RNA为模板,用RT-PCR方法扩增了含有复制酶(NIb)基因的DNA片段,将其克隆到质粒pGM-T载体上并进行了序列分析。结果表明,NIb基因由1563个碱基组成,编码521个氨基酸并含有高度保守序列GDD。NIa/NIb和NIb/CP交界处的蛋白酶切割位点分别为Q/C和Q/A。与国外报道的SCMV亚组几个株系分离物相比,NIb基因(福建分离物)的核苷酸和氨基酸序列同源性分别为57.8%~86.9%和60.9%~95.2%,其中与SCMV-SA株系的核苷酸及氨基酸序列同源性则高达86.9%和95.2%。 相似文献
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蝉拟青霉是一种常见的昆虫病原真菌,被广泛应用于生物防治。本研究根据GenBank中已登录的淡紫拟青霉、粉拟青霉、球孢白僵菌和金龟子绿僵菌的类枯草杆菌蛋白酶基因序列的同源性比较,以它们高度保守的核苷酸序列设计一对引物,采用RT-PCR和3'/5'-RACE相结合的方法,从蝉拟青霉中克隆出完整的类枯草杆菌蛋白酶(subtilisin-like protease)cDNA基因序列。cDNA全序列为2 031 bp,该序列5'-端和3'-端的非编码序列长度分别为170 bp和262 bp,开放阅读框为1 599 bp,编码532个氨基酸,信号肽长度为18个氨基酸,前肽长度为133个氨基酸。该基因编码的蛋白序列与虫草棒束孢(Isaria farinosa)、球孢白僵菌(Beauveria bassiana)、蛹虫草(Cordyceps militaris)和哈茨木霉(Trichoderma harzianum)类枯草杆菌蛋白酶有较高的同源性,同源性分别为88%、88%、89%和71%。成熟蛋白具有典型的丝氨酸蛋白酶活性位点,同时有5个半胱氨酸,4个潜在的N-糖基化位点,位于细胞的液泡中与分泌途径相关,二级结构中以α-螺旋和无规则卷曲为主。 相似文献
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X-ray structure of the GCN4 leucine zipper, a two-stranded, parallel coiled coil 总被引：107，自引：0，他引：107