骨肉瘤相关新分子5D3Ag的研究

目的：自建的抗人骨肉瘤单克隆抗体mAb5D3经鉴定有很好的骨肉瘤细胞特异性，并且已利用单抗纯化出相应的骨肉瘤相关抗原5D3Ag纯品，研究目的是测定5D3Ag氨基酸序列，鉴定5D3Ag是否为一新发现的骨肉瘤相关抗原。方法：用SDS-PAGE法分析5D3Ag纯度和分子量，并做免疫印迹分析，用半干式转移法将5D3Ag转移到氨基酸测序膜上，测定其氨基酸序列，在蛋白质序列中比较分析，初步推断此抗原的性质及是否为新发现的骨肉瘤相关抗原。结果：5D3Ag经SDSPAGE分析达到了电泳纯，分子量为43kD；Western Blot分析显示5D3Ag可以与mAb5D3结合；5D3Ag N端10个氨基酸序列为：门冬酰胺、谷氨酰胺、甘氨酸、丝氨酸、组氨酸、甘氨酸、丝氨酸、谷氨酸、丙氨酸、谷氨酰胺(NQGSHGSEAQ)。结论：5D3Ag从其分子量来看与以往文献所报道的骨肉瘤相关抗原的分子量都不相同；氨基酸序列结果查询分析，与蛋白质库中已知的蛋白质同源性很低，由此推断5D3Ag可能是一种新的骨肉瘤相关抗原。     

自制肝素亲和柱分离纯化载脂蛋白H及其抗体制备与鉴定

目的：自制肝素-琼脂糖6B亲和柱提纯人血清载脂蛋白H（apoH）,免疫制备多克隆抗体,为大量制备与进一步研究做准备。方法：利用间接还原胺化法制备亲和层析柱,并优化反应条件。运用高氯酸沉淀、离子交换及亲和层析从人血清中纯化抗原,制备兔源多克隆抗体。结果：自制亲和柱肝素结合量约5mg/g（介质体积）。纯化的抗原经SDS-PAGE鉴定分子量约50kD,无杂带;16种氨基酸组成分析结果与报道一致。多克隆抗体与购置的国外抗体一样,在进行ELISA与dot-ELISA时与小牛血清白蛋白有交叉反应;但在变性且还原的条件下,Western blot结果显示无交叉反应。结论：自制亲和柱成本低、亲和性好、肝素结合稳定,用之分离纯化得到了高纯度apoH;兔多克隆抗体用于检测血清中载脂蛋白H含量时需进一步纯化。     

广西眼镜王蛇毒杂合性酸性磷脂酶A2的基因克隆与序列分析

目的：研究广西眼镜王蛇毒杂合性酸性磷脂酶A2（APLA2）的基因克隆与序列分析。方法：从广西眼镜王蛇毒腺中提取总RNA，根据种属关系接近的台湾眼镜蛇毒APLA2两端非翻译区的保守序列设计引物，利用RT－PCR进行体外扩增，获得磷脂酶A2基因，克隆至pMD18-T载体，经测序筛选出APLA2－1，APLA2－2及一个新的酸性磷脂酶A2（命名为APLA2－3）。根据测序结果确定了APLA2－3基因的全序列，并由此推导编码的氨基酸序列。结果：利用Antheprot 4.3c蛋白质序列分析软件包计算它的等电点为4．885，相对分子质量为16．543kD，并预测了它的二级结构和部分理化性质，同源性比较表明，APLA2－3的1－39位氨基酸残基序列与APLA2－2相同，其同源性为64％，而40－108位氨基酸残基序列为APLA2－1相同，其同源性为69％，10位氨基酸残基序列皆不同于这两种APLA2。结论：揭示了APLA2具有基因多样性，可能与物种进化和生物活性有关，并为进一步研究PLA2的结构与功能的关系提供更多的信息。     

蛋白质和多肽的N端测序技术研究进展

氨基酸序列测定是了解蛋白质性质和功能的重要途径，N端区域又是蛋白质及多肽重要的结构和功能部位，其序列特异性很高，通过N端的少数几个氨基酸残基就可以对人多数蛋白质进行鉴定^[1]。例如，可以通过对蛋白质和多肽类约物的N端进行人工修饰（如环化修饰、甲基化修饰等），提高其降解稳定性延长药效^[2-3].因此N端肽段的鉴定具有非常重要的意义，本文对近年来蛋白质和多肽N端测序技术及办法进行了综述。     

重组幽门螺杆菌热休克蛋白A亚单位的高效表达及其初步纯化

目的 在大肠杆菌中高效表达幽门螺直菌的热休克蛋白A基因（hspA)，并对其初步纯化。方法 用巢式PCR扩增hspA基因。经测序证实后，克隆于表达载体pIM-1中，转化大肠杆菌。以SDS－PAGE和免疫印迹分析目的蛋白的表达，并测定N－端氨基酸的序列。采用固相镍离子亲和层析，对重组hspA进行初步纯化。结果 扩增的hspA基因为357bp，并在大肠杆菌中得到高效可溶性表达。重组蛋白的表达量最高可达细菌总蛋白的60．5％。免疫印迹及氨基酸测序结果证实，表达产物为幽门螺杆菌hspA亚单位。固相镍离子亲和层析初步纯化的重组HspA的纯度为87．8％，结论 hspA亚单位的高效表达与初步纯化，为批量获得Hp亚单位抗原打下了基础。     

鼠疫F1蛋白原核分泌性表达及鉴定

目的构建重组质粒,在大肠杆菌中表达鼠疫菌F1抗原。方法用PCR方法扩增出带有信号肽的F1基因,将其克隆到表达载体pET30a(+)上,转化大肠杆菌BL21(DE3);用IPTG诱导目的基因表达,层析方法纯化F1蛋白,测定其分子量、等电点、N末端氨基酸序列,用Westernblot法检测其抗原性。结果根据双酶切和DNA测序结果显示,F1基因成功连接到表达载体pET30a(+)中,F1蛋白主要为分泌性可溶表达。测定纯化后F1蛋白的相对分子量约为15.6kD,等电点为4.15,N末端氨基酸序列与理论序列一致。经Westernblot鉴定,能被兔抗鼠疫菌EV株血清识别。结论成功克隆并构建了F1蛋白分泌性原核表达系统,所表达的重组F1蛋白具有较好的抗原性,为新型鼠疫疫苗研制提供基础。     

与IL-2受体β链相作用的IL-15的克隆

作者在检测猴肾表皮细胞系cv-1/EBNA上清的细胞因子活性过程中发现,这些细胞产生一种能维持IL-2依赖细胞系CILL增殖的可溶性细胞因子,经一系列分离纯化过程表明该因子为大约14～15kD的蛋白质,并对其N端33个氨基酸残基直接测序。基于所测AA序列,作者采用简并寡聚核苷酸     

apoH基因多态性与脑卒中的相关性研究及其对血脂的影响

目的：探讨载脂蛋白H（apolipoprotein H,apoH）基因第8外显子G1025C（Try316Ser）多态性与长沙地区汉族人脑卒中的关系及其对血 脂的影响。方法：采用PCR－单链构象多态技术和DNA直接测序法检测长沙地区汉族260例脑卒中患者、20个脑卒中家系成员和100名健康对照者的apoH基因第8外显子G1025C（Try316Ser）多态性；酶联免疫吸附法检测抗磷脂抗体水平；酶法测定总胆固醇（TC）、甘油三酯（TG）、高密度脂蛋白胆固醇（HDL－C）、低密度脂蛋白胆固醇（LDL－C），免疫比浊法测定apoA-I及apo B100，酶联免疫吸附法测定脂蛋白a血清水平。结果：长沙地区汉族人apoH基因G1025C（Try316Ser）多态存在GG、GC两种基因型，脑卒中组及其各亚组G1025C（Try316Ser）多态基因频率分布与对照组比较差异无显著性（P＞0．05）；分析不同基因型对血脂、脂蛋白水平的影响，发现脑梗塞组和对照组GC基因型血清TG水平均明显高于GG基因型（P＜0．05）。结论：长沙地区汉族人apoH基因G1025C（Try316Ser）多态性可能与脑卒中的易患性无关，但与血脂代谢有一定关联。     

人era的结构特点分析及其定点突变体的构建

目的：构建最近克隆的人era基因的定点突变体。方法：利用数据库对era的结构特点进行分析，在此基础上用改良的重叠延伸法分别构建人EraN端和C端的定点突变体。结果：获得了分别针对人EraN端TGP结合结构域（位于29－36氨基酸残基）和C端具有RNA结合活性的 KH结构域（位于297－340氨基酸残基）的定点突变体。结论:人era定点突变体的构建为进一步的功能研究奠定了基础。     

重组人IL—4 cDNA及纯化蛋白的鉴定

构建了和且人白细胞介素４（ｒｈＩＬ－４）表达质粒ｐＢＶ２２０／ｒｈＩＬ－４ａ，并在Ｅ．ｃｏｌｉ中高效表达。经核苷酸序列分析，测出ｒｈＩＬ－４ ｃＤＮＡ全序列与国外发表的ｈＩＬ－４ ｃＤＮＡ序列完全相同。其纯化蛋白产品经分子量测定，Ｗｅｓｔｅｒｎ印迹分析，等电点分析，Ｎ－端氨基酸序列测定，比活性等测定证明，均符合ｒｈＩＬ－４。     

Aminopeptidase N in Sera of Healthy Subjects Is a Different N-Terminal Processed Derivative from the One Obtained from Maternal Serum

A major aminopeptidase present in normal human serum was purified to homogeneity as a 150-kDa molecular species. Western blotting confirmed the binding of an anti-aminopeptidase N antibody to the protein. The N-terminal amino acid sequence of the enzyme was determined. The first 13 amino acids of the enzyme completely matched amino acids 59–71 of the sequence predicted from the human intestinal aminopeptidase N cDNA nucleotide sequence. As reported previously, aminopeptidase N from maternal serum had 68 fewer amino acid residues at the N-terminus than the enzyme obtained from detergent-solubilized membranes. The results indicate that aminopeptidase N in normal serum is a different N-terminal processed derivative from that obtained from maternal serum.     

Role of the N-terminal regions of hog C3a, C5a and C5a-desArg in their biological activities

The N-terminal regions of the complement peptides C3a, C5a and C5a-desArg (purified from yeast-activated hog serum) were gradually shortened by incubation with leucine amino peptidase. This treatment led to the following changes in the biological activities of these peptides: the potencies of C5a and C5a-desArg in aggregation of human polymorphonuclear leukocytes and of guinea-pig platelets, and their ability to deactivate these cells were gradually diminished; the chemotactic effect of C5a-desArg on human leukocytes was similarly lowered, while the chemotactic potency of C5a was even increased up to the loss of the first 12 N-terminal amino acids. However, after removal of the whole N-terminal region (i.e. 20 amino acids distal of the first disulfide bridge) the potency of both peptides was decreased to a few percent. In contrast, C3a totally lost its platelet-aggregating as well as deactivating activity already after cleavage of 10-15 N-terminal amino acids by LAP. On leukocytes, on the other hand, C3a retained some activity even after the loss of the whole N-terminal region. These results indicate that the N-terminal regions play an important role for biological activities of the three complement peptides, possibly by stabilizing the optimal conformation of their C-terminal regions which contain the receptor-activating domains.     

Amino acid sequence studies of human C4b-binding protein: N-terminal sequence analysis and alignment of the fragments produced by limited proteolysis with chymotrypsin and the peptides produced by cyanogen bromide treatment

Treatment of human C4b-binding protein (C4BP) with cyanogen bromide gave five major peptides and limited proteolysis with chymotrypsin yielded two fragments. The yields, apparent mol. wts and N-terminal amino acid sequences of these peptides and fragments indicates that in dissociating conditions, after reduction of disulphide bonds, C4BP is composed of only one type of polypeptide chain of approx. 70,000 mol. wt. The amino acid sequence data obtained, which accounts for over 55% of the total sequence, allows an alignment of the cyanogen bromide peptides. In addition the amino acid sequence data indicates that the 70,000-dalton polypeptide chain of C4BP contains nine internal homology regions, each 60 amino acids long, which would account for 540 of the expected 600 amino acids in C4BP. Similar internal homology regions are found within the Ba region of factor B [Morley and Campbell, EMBO J. 3, 153-157 (1984)] and it is of interest that the regions found in C4BP are homologous to those found in Ba.     

A comparative review of the structure and biosynthesis of thyroglobulin

Thyroglobulin, the major iodoglycoprotein of the thyroid (Mr 669 kDa) has a sedimentation coefficient of 19 S and an isoelectric point (pI) of 4.4-4.7. The protein has been isolated and purified from saline extracts of the gland of several animal species, by methods such as ammonium sulfate fractionation, DEAE-cellulose chromatography and Sepharose 4B/6B gel-filtration. DEAE-cellulose chromatography of thyroglobulin from many species, by linear gradient, yielded a complex elution pattern, while camel thyroglobulin showed only a major and minor peak. As an iodoprotein, the protein has 0.1-2.0% iodine. The amino acid and iodoamino acid composition of thyroglobulins, in general, is similar. However, a high thyroxine content (15 mol/mol protein) has been noted for buffalo species. Asparagine or aspartic acid has been reported as the major N-terminal amino acid for thyroglobulins of several animal species whereas glutamic acid is the sole N-terminal amino acid for buffalo thyroglobulin. As a glycoprotein, thyroglobulin contains 8-10% total carbohydrate with galactose, mannose, fucose, N-acetyl glucosamine and sialic acid residues. The carbohydrate in the protein is distributed as two distinct units, A and B. In addition, human thyroglobulin has carbohydrate unit C. The occurrence of sulfate and phosphate as Gal-3-SO4 and Man-6-PO4, respectively, has been reported in few species. The quaternary structure of native thyroglobulin is comprised of two equal sized subunits of 330 kDa. However, the protein appears to contain 4-8 non-identical units in few species. The synthesis of thyroid hormones occurs in the matrix of the protein and is regulated by pituitary thyrotropin. The role of tyrosine residues 5 and 130 in thyroxine synthesis has been well documented.     

Identification of structural mutations in the fifth domain of apolipoprotein H (beta 2-glycoprotein I) which affect phospholipid binding

Apolipoprotein H (apoH), also known as beta 2-glycoprotein-I, is considered to be a cofactor for the binding of certain antiphospholipid autoantibodies to negatively charged phospholipids. Genetically determined structural abnormalities in the lipid binding domain(s) of apoH can affect its ability to bind lipid and consequently the production of the autoantibodies. In this study we have identified two common structural mutations at codons 316 and 306 in the fifth domain of apoH which rendered apoH unable to bind to negatively charged phosphatidylserine (PS). The missense mutation at codon 316 (TGG --> TCG) replaces Trp316 with Ser316 and disrupts the integrity of four highly conserved hydrophobic amino acids sequence at positions 313-316, which is a potential protein-lipid hydrophobic interaction site. The missense mutation at codon 306 (TGC --> GGC) involves the substitution of Cys306 by Gly306 which causes the disruption of a disulfide bond between Cys281 and Cys306 and affects the normal configuration of the fifth domain of apoH that appears to be critical for clustering positively charged amino acids along with four hydrophobic amino acids sequence. ApoH from the two homozygotes (Ser316/Ser316) and all seven compound heterozygotes (Ser316/Gly306) failed to bind to PS; all heterozygotes at one or the other sites and wild type showed normal PS binding. These data indicate that the fifth domain of apoH harbors the lipid binding region. An estimated 2 million Caucasians in the United States, who are compound heterozygotes for the two mutations, may be precluded from producing apoH-dependent antiphospholipid autoantibodies.      

Factor C3f is a spasmogenic fragment released from C3b by factors I and H: the heptadeca-peptide C3f was synthesized and characterized

C3f, a heptadeca-peptide having the amino acid sequence of NH2-Ser-Ser-Lys-Ile-Thr-His-Arg-Ile-His-Trp-Glu-Ser-Ala-Ser-Leu-Leu-Arg- COOH, is liberated during the catabolic degradation of C3b in serum. The amino acid sequence of C3f is known both from the cDNA-derived structure of C3 and from protein analysis after isolation of the natural factor. C3f was synthesized by solid phase peptide synthesis. Both natural and synthetic C3f had identical retention times by RP-18 high performance liquid chromatography (HPLC) analysis and the respective amino acid compositions agreed with the expected theoretical values. C3f, but not des-Arg-C3f, was weakly spasmogenic inducing contraction of guinea pig ileum at a level of 5-10 x 10(-6) M. Since C3f and C3a were cross-tachyphylactic, it was concluded that these two spasmogens compete for the same receptors. Both C3f and des-Arg-C3f at concns of 1-4 x 10(-4) M enhanced vascular permeability in guinea pig skin. These observations further suggest that C3f functionally resembles C3a anaphylatoxin. Formation of C3f in human serum following CVF activation of C3 could be demonstrated by radioimmunoassay (RIA). Digestion of C3f with purified human serum carboxypeptidase N produced C3f-desArg. These observations suggest that when serum complement protein C3 undergoes conversion to C3b, further degradation by Factors H and I readily generates C3f. C3f is a weak spasmogen that functions like C3a anaphylatoxin and C3f-desArg is a major metabolite in serum.     

Comparative studies on tree pollen allergens. X. Further purification and N-terminal amino acid sequence analyses of the major allergen of birch pollen (Betula verrucosa)

The previously isolated major allergen of birch pollen (fraction BV45), Int. Archs Allergy appl. Immun. 68: 70-78 (1982), was further purified by recycling chromatography. The purified preparation was run on a high-performance liquid chromatography (HPLC) TSK-G-2000 gel filtration chromatography column and, finally, on paper high-volt electrophoresis. The protein recovered met the homogeneity criteria required for performing the N-terminal sequence analysis. The allergenic and antigenic reactivities of the HPLC-purified protein, designated BV45B, was examined. A single homogeneous precipitation line in crossed immunoelectrophoresis (CIE) was shown. Specific IgE-inhibition tests and immuno-autoradiographic prints indicated that this allergen could bind reaginic IgE specificially and with good affinity. The homogeneity of BV45B was examined by isoelectric focusing (IEF). Several minor bands of pI differences of less than 0.1 units were visible, demonstrating the existence of some molecular variants of this protein. The N-terminal sequence analysis of the molecule was performed, and the following four amino acids were tentatively shown by sequential cleavage: NH2-Ala-Gly-Ile-Val-. The demonstration of one dominant N-terminal 1-dimethyl-amino-5-naphthalene sulphonyl (DNS)-amino acid by polyamide thin-layer chromatography at each sequence step confirmed that the N-terminal residue of the protein was not blocked; the heterogeneity shown by the IEF system was merely due to the presence of several homologous polymorphic proteins with identical N-terminal amino acid, the adequacy of the purification repertoire used.     

Interleukin-1 receptor antagonist in inflammatory exudate cells of rabbits. Production, purification and determination of primary structure

A rabbit interleukin-1 (IL-1) inhibitor in inflammatory peritoneal exudate cells was purified to apparent homogeneity. This inhibitor was extracted from exudate cells of the 24-hr stage of casein-induced peritoneal inflammation and purified using isoelectrofocusing (IEF), gel filtration, followed in this order by high-performance liquid chromatography (HPLC) steps with hydroxylapatite and anionic ion exchanger. The purified factor showed a single band on silver-stained SDS-PAGE. This molecule of MW 19,000 and pI 5.5 inhibited the binding of both IL-1 alpha and beta to receptors on a thymoma cell line, EL-4 and a B-cell line, 70Z/3. We determined its primary structure by a combination of peptide chemistry and molecular cloning. The inhibitor was synthesized as a precursor composed of 177 amino acids and was processed to a mature molecule of 143 amino acids. The N-terminal amino acid of the mature inhibitor was N-acetyl-methionine residue. The deduced amino acid sequence of the inhibitor showed a 77% homology to the human IL-1 receptor antagonist (IL-1Ra) and essentially the same mode of action as seen with human IL-1Ra. We consider that this inhibitor is a rabbit counterpart of human IL-1Ra, although there are differences with respect to the molecular structure; the N-terminus of the mature rabbit IL-1Ra at a position of nine amino acids downstream from that of human IL-1Ra.     

Flavoxobin,a serine protease from Trimeresurus flavoviridis (habu snake) venom,independently cleaves Arg726-Ser727 of human C3 and acts as a novel,heterologous C3 convertase

We have recently shown that crude Trimeresurus flavoviridis (habu snake) venom has a strong capability for activating the human alternative complement system. To identify the active component, the crude venom was fractionated and purified by serial chromatography using Sephadex G-100, CM-cellulose C-52, diethylaminoethyl-Toyopearl 650M, and Butyl-Toyopearl, and the active fractions were evaluated by the C3a-releasing and soluble membrane attack complex-forming activities. Two peak fractions with the highest activities were detected after gel filtration and ion exchange chromatography, and the first fraction was purified to homogeneity. The homogeneous protein was examined for its N-terminal amino acid sequence by Edman degradation. The determined sequence of 25 amino acids completely coincided with that of a previously reported serine protease with coagulant activity, flavoxobin, purified from the same snake venom. To elucidate the molecular mechanism of the complement activation, the reactive products of the mixture of the purified human C3 and flavoxobin were examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The digesting pattern revealed that flavoxobin cleaves the alpha chain of the C3 molecule into two fragments. The N-terminal amino acid sequences for the remnant fragments of C3 disclosed that flavoxobin severs the human C3 at the Arg726-Ser727 site to form C3b and C3a the way C3bBb, the human alternative C3 convertase, does. In conclusion, flavoxobin acts as a novel, heterologous C3 convertase that independently cleaves human C3 and kick-starts the complement cascade.