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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De novo design, expression, and characterization of Felix: a four-helix bundle protein of native-like sequence 总被引：30，自引：0，他引：30
The protein Felix was designed de novo to fold into an antiparallel four-helix bundle of specific topology. Its sequence of 79 amino acid residues is not homologous to any known protein sequence, but is "native-like" in that it is nonrepetitive and contains 19 of the 20 naturally occurring amino acids. Felix has been expressed from a synthetic gene cloned in Escherichia coli, and the protein has been purified to homogeneity. Physical characterization of the purified protein indicates that Felix (i) is monomeric in solution, (ii) is predominantly alpha-helical, (iii) contains a designed intramolecular disulfide bond linking the first and fourth helices, and (iv) buries its single tryptophan in an apolar environment and probably in close proximity with the disulfide bond. These physical properties rule out several alternative structures and indicate that Felix indeed folds into approximately the designed three-dimensional structure. 相似文献
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Mouse immunoglobulin D: messenger RNA and genomic DNA sequences 总被引：26，自引：0，他引：26
The molecular structure of a mouse immunoglobulin D from a plasmacytoma tumor and that of the normal mouse gene coding for immunoglobulin D are presented. The DNA sequence results indicate an unusual structure for the tumor delta chain in two respects: (i) Only two constant (C) region domains, termed C delta 1 and C delta 3 by homology considerations, are found; the two domains are separated by an unusual hinge region C delta H that lacks cysteine residues and thus cannot provide the covalent cross-links between heavy chains typically seen in immunoglobulins. The two domains and hinge are all coded on separate exons. (ii) At the carboxyl end of the delta chain there is a stretch of 26 amino acids that is coded from an exon located 2750 to 4600 base pairs downstream from the rest of the gene. Analogy with immunoglobulin M suggests that this distally coded segment C delta DC may have a membrane-binding function; however, it is only moderately hydrophobic. A fifth potential exon (C delta AC), located adjacent to the 3' (carboxyl) end of C delta 3, could code for a stretch of 49 amino acids. The tumor's expression of the delta gene may be aberrant, but the simplest interpretation would be that this tumor expresses one of the several biologically significant forms of the delta chain. 相似文献
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黄河三角洲河蚬软体部营养成分的分析及评价 总被引：1，自引：0，他引：1
对黄河三角洲流域分布的河蚬软体部营养成分进行了分析,综合评定其营养价值.结果表明,河蚬软体部干样中,粗蛋白、粗脂肪、灰分含量分别为53.90%、8.90%和1.33%;共测到了17种氨基酸,必需氨基酸占氨基酸总量的37.44%,大部分必需氨基酸分(AAS)在40分以上,含硫氨基酸(半胱氨酸+蛋氨酸)为第一限制性氨基酸, 色氨酸得分最高为124.00分;共分析了10种主要脂肪酸,其中EPA、DHA含量分别占7.62%和8.61%.河蚬富含钙、钠、镁、钾、铁等11种无机元素,维生素A、B含量也较丰富.对紫彩血蛤的脂肪酸组成及含量进行了检测, 其中EPA、DHA含量分别占15.23%和6.45%. 相似文献
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Identification of paramyosin as schistosome antigen recognized by intradermally vaccinated mice 总被引：20，自引：0，他引：20
Mice immunized intradermally with extracts of Schistosoma mansoni in combination with the adjuvant BCG are significantly protected against subsequent infection with living larval forms of the parasite. Remarkably, these vaccinated animals produce antibodies predominantly against a single parasite protein of molecular weight 97 kilodaltons (Sm-97). A complementary DNA that encodes about half of the Sm-97 molecule has now been cloned and sequenced. Analysis of the deduced amino acid sequence reveals a protein containing periodic repeats of hydrophobic amino acids characteristic of an alpha-helical coiled-coil structure. The deduced amino acid composition of the cloned gene and several properties of the native protein are similar to that of paramyosin, an alpha-helical protein that forms the core for myosin filaments in invertebrate muscle. Paramyosin was isolated from Schistosoma mansoni adult worms and antibodies to Sm-97 were shown to react with this molecule as well as with a known paramyosin from molluscan muscle. 相似文献
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Replacements of Pro86 in phage T4 lysozyme extend an alpha-helix but do not alter protein stability 总被引：10，自引：0，他引：10
T Alber J A Bell D P Sun H Nicholson J A Wozniak S Cook B W Matthews 《Science (New York, N.Y.)》1988,239(4840):631-635
To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations. 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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The structure of rat preproatrial natriuretic factor as defined by a complementary DNA clone 总被引：14，自引：0，他引：14
C E Seidman A D Duby E Choi R M Graham E Haber C Homcy J A Smith J G Seidman 《Science (New York, N.Y.)》1984,225(4659):324-326
The structure of rat preproatrial natriuretic factor ( preproANF ) was determined by nucleotide sequence analysis of an ANF complementary DNA clone. PreproANF is composed of a hydrophobic leader segment (20 amino acids), a precursor containing one glycosylation site (106 amino acids), and ANF (24 amino acids). Atrial natriuretic factor is located at the carboxyl terminus of the precursor molecule. The human, mouse, and rat genomes each contain a single ANF gene which is highly conserved. 相似文献
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霍山石斛不同部位中必需微量元素与必需氨基酸的相关性研究 总被引：3，自引：1，他引：3
求文对名贵中药材霍山石斛各部位中必需微量元素和必需氨基酸的含量进行了测定，对人体和植物共同的必需微量元素与人体必需氨基酸间的相关性进行了研究。结果发现，Ｃｕ、Ｚｎ、Ｆｅ与必需氨基酸呈负相关；Ｍｇ、Ｃａ、Ｍｎ与必需氨基酸呈正相关。欲提高霍山石斛中必需氨基酸含量，建议少施Ｃｕ、Ｚｎ、Ｆｅ粪肥料，适当多施Ｍｇ、Ｃａ、Ｍｎ类微肥。 相似文献
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Conserved folding in retroviral proteases: crystal structure of a synthetic HIV-1 protease 总被引：57，自引：0，他引：57
A Wlodawer M Miller M Jaskólski B K Sathyanarayana E Baldwin I T Weber L M Selk L Clawson J Schneider S B Kent 《Science (New York, N.Y.)》1989,245(4918):616-621
The rational design of drugs that can inhibit the action of viral proteases depends on obtaining accurate structures of these enzymes. The crystal structure of chemically synthesized HIV-1 protease has been determined at 2.8 angstrom resolution (R factor of 0.184) with the use of a model based on the Rous sarcoma virus protease structure. In this enzymatically active protein, the cysteines were replaced by alpha-amino-n-butyric acid, a nongenetically coded amino acid. This structure, in which all 99 amino acids were located, differs in several important details from that reported previously by others. The interface between the identical subunits forming the active protease dimer is composed of four well-ordered beta strands from both the amino and carboxyl termini and residues 86 to 94 have a helical conformation. The observed arrangement of the dimer interface suggests possible designs for dimerization inhibitors. 相似文献
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mTORC1 senses lysosomal amino acids through an inside-out mechanism that requires the vacuolar H(+)-ATPase 总被引：3，自引：0，他引：3
Zoncu R Bar-Peled L Efeyan A Wang S Sancak Y Sabatini DM 《Science (New York, N.Y.)》2011,334(6056):678-683
The mTOR complex 1 (mTORC1) protein kinase is a master growth regulator that is stimulated by amino acids. Amino acids activate the Rag guanosine triphosphatases (GTPases), which promote the translocation of mTORC1 to the lysosomal surface, the site of mTORC1 activation. We found that the vacuolar H(+)-adenosine triphosphatase ATPase (v-ATPase) is necessary for amino acids to activate mTORC1. The v-ATPase engages in extensive amino acid-sensitive interactions with the Ragulator, a scaffolding complex that anchors the Rag GTPases to the lysosome. In a cell-free system, ATP hydrolysis by the v-ATPase was necessary for amino acids to regulate the v-ATPase-Ragulator interaction and promote mTORC1 translocation. Results obtained in vitro and in human cells suggest that amino acid signaling begins within the lysosomal lumen. These results identify the v-ATPase as a component of the mTOR pathway and delineate a lysosome-associated machinery for amino acid sensing. 相似文献
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Gamblin SJ Haire LF Russell RJ Stevens DJ Xiao B Ha Y Vasisht N Steinhauer DA Daniels RS Elliot A Wiley DC Skehel JJ 《Science (New York, N.Y.)》2004,303(5665):1838-1842
The 1918 influenza pandemic resulted in about 20 million deaths. This enormous impact, coupled with renewed interest in emerging infections, makes characterization of the virus involved a priority. Receptor binding, the initial event in virus infection, is a major determinant of virus transmissibility that, for influenza viruses, is mediated by the hemagglutinin (HA) membrane glycoprotein. We have determined the crystal structures of the HA from the 1918 virus and two closely related HAs in complex with receptor analogs. They explain how the 1918 HA, while retaining receptor binding site amino acids characteristic of an avian precursor HA, is able to bind human receptors and how, as a consequence, the virus was able to spread in the human population. 相似文献
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为了解贵州黔东南棘蛙的肌肉营养价值,采用常规氨基酸分析方法测定黔东南棘胸蛙、棘侧蛙和棘腹蛙3种野生棘蛙肌肉的氨基酸组成与含量,并以鸡蛋蛋白质为标准蛋白,以WHO/FAO氨基酸参考模式为标准对其进行氨基酸营养评价。结果表明:黔东南3种野生棘蛙肌肉的氨基酸组成一致,其中含有苏氨酸、缬氨酸、蛋氨酸、异亮氨酸、亮氨酸、苯丙氨酸和赖氨酸7种人体必需氨基酸,非必需氨基酸5种,天冬氨酸、谷氨酸、甘氨酸和丙氨酸4种鲜味氨基酸。棘胸蛙、棘腹蛙和棘侧蛙肌肉中氨基酸总量分别为84.19%、87.43%和86.12%。必需氨基酸含量占总氨基酸含量的比值分别为39.79%、40.07%和39.06%,在蛙科动物中均属于较高水平。3种棘蛙肌肉中,均以谷氨酸的含量最高,天冬氨酸的含量次之,蛋氨酸含量最低。氨基酸评分(AAS)和化学评分(CS)表明,棘蛙肌肉中第一限制性氨基酸为蛋氨酸,第二限制性氨基酸为缬氨酸。必需氨基酸指数(EAAI)显示,棘胸蛙为86.72、棘腹蛙为89.79、棘侧蛙为86.22。综合各项指标分析,贵州黔东南3种野生棘蛙具有较高的经济价值。 相似文献
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为了解玉米自交系的氨基酸品质性状,筛选出高游离氨基酸含量的自交系,为玉米育种和品质改良提供优质种质资源。试验利用HPLC方法,对高赖氨酸玉米‘Opaque-2’和13个常用玉米自交系的16种游离氨基酸含量进行了检测。结果表明,‘Opaque-2’材料中检测出15种游离氨基酸,总游离氨基酸含量达干物质总量的3.42%,赖氨酸含量达0.28%。13个常用自交系除1个含量稍高外,其余12个自交系游离氨基酸和必需氨基酸含量都很低,赖氨酸含量仅是‘Opaque-2’的0～34%。该结果说明目前常用玉米主要品种亲本自交系的必需氨基酸营养品质基因是低水平类型。 相似文献
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Microtubule-associated protein MAP2 shares a microtubule binding motif with tau protein 总被引：57，自引：0，他引：57
The microtubule-associated protein MAP2 is a prominent large-sized component of purified brain microtubules that, like the 36- to 38-kilodalton tau proteins, bears antigenic determinants found in association with the neurofibrillary tangles of Alzheimer's disease. The complete sequence of mouse brain MAP2 was determined from a series of overlapping cloned complementary DNAs. The sequence of the carboxyl-terminal 185 amino acids is very similar (67 percent) to a corresponding region of tau protein, and includes a series of three imperfect repeats, each 18 amino acids long and separated by 13 or 14 amino acids. A subcloned fragment spanning the first two of the 18-amino acid repeats was expressed as a polypeptide by translation in vitro. This polypeptide copurified with microtubules through two successive cycles of polymerization and depolymerization, whereas a control polypeptide derived from the amino-terminal region of MAP2 completely failed to copurify. These data imply that the carboxyl-terminal domain containing the 18-amino acid repeats constitutes the microtubule binding site in MAP2. The occurrence of these repeats in tau protein suggests that these may be a general feature of microtubule binding proteins. 相似文献
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A unique transfer RNA (tRNA)/aminoacyl-tRNA synthetase pair has been generated that expands the number of genetically encoded amino acids in Escherichia coli. When introduced into E. coli, this pair leads to the in vivo incorporation of the synthetic amino acid O-methyl-l-tyrosine into protein in response to an amber nonsense codon. The fidelity of translation is greater than 99%, as determined by analysis of dihydrofolate reductase containing the unnatural amino acid. This approach should provide a general method for increasing the genetic repertoire of living cells to include a variety of amino acids with novel structural, chemical, and physical properties not found in the common 20 amino acids. 相似文献