四连接素蛋白的研究进展

研究四连接素( tetranectin,TN)的历史已近30年,并且发现TN与多种疾病有关,但是,至目前为止,TN的功能及作用机制仍不清楚.Pubmed文献检索显示,有关TN的文献报道有逐年增多趋势,这提示TN蛋白越来越受关注.     

对双亲/孩子结构连接算法的研究与改进

结合区间编码和结点模型映射方法提出一种用于关系数据库的扩展存储模式.通过按广度优先遍历XML树实现对双亲/孩子关系结构连接算法的改进.改进后的算法降低了内存空间的开销,缩小了列表的扫描范围,明显提高了查找匹配速度,达到了查询优化的目的.     

流感病毒血凝素共价抑制剂的设计、合成及活性研究（英文）

近年来流感频发,针对传统靶点抗流感药物(如扎那米韦和奥司他韦)的耐药病毒大量出现,迫切需求开发新靶点、新作用机制的抗流感药物。本研究针对流感病毒血凝素(HA)底物结合位点附近的赖氨酸(Lys133和Lys222),设计了系列具有共价结合潜力的唾液酸类化合物(1a–1h)。活性研究表明该系列化合物对两种流感病毒HA蛋白的结合力较母体化合物唾液酸(SA)有明显提升,其中化合物1d与阳性化合物2,6-唾液酸乳糖胺(2,6-SLN)持平(K_D=38.2和39.6μM);该系列化合物安全无毒(对MDCK细胞CC₅₀>1 m M),其中化合物1d可有效抑制流感病毒在MDCK细胞中的复制。本研究提出了基于流感病毒HA的共价抑制新策略,深入发掘有望获得新型强效HA抑制剂。     

K-RASG12C小分子共价抑制剂的研究进展

Ras原癌基因的突变是人类癌症中最常见的激活突变,驱动人类30％肿瘤的发生与发展,因此人们一直希望能够研发出靶向RAS蛋白的抗肿瘤药物,但进展缓慢.直至最近两年,随着首个K-RASG12C共价抑制剂AMG-510进入临床试验,直接靶向RAS蛋白的药物研发才逐渐显露出希望的曙光.本文主要介绍K-RASG12C小分子共价抑...     

蛋白水解靶向嵌合体(PROTAC)连接链优化的研究进展

近年来,具有高度选择性和效能的靶向蛋白降解技术在药学中的潜在应用已逐步受到关注。其中,起到诱导靶蛋白降解作用的蛋白水解靶向嵌合体(proteolysis targeting chimeras,PROTAC)是近年来药物研发领域的新热点之一。目前,PROTAC的研究主要围绕理性合理设计PROTAC分子、发现新型E3泛素连接酶配体和提升PROCTAC分子成药性等方面,相关理论发展迅速。本文聚焦于PROTAC分子中的连接链部分,从连接链的长度、连接链与配体的结合位点以及连接链的化学结构三个角度总结了近年来连接链的差异如何影响E3酶-PROTAC-靶蛋白三元复合物生成的相关研究进展,并进一步讨论了连接链差异对于PROTAC分子的降解效率和选择性的影响。     

BitTorrent协议Choking/Unchoking机制的度量和分析

BitT0rrent是一个用于内容分发的P2P协议,现在已经发展成为互联网的一项重要的应用.本文从性能的角度,度量BitTorrent的行为,解释BitTorrent协议的关键元素,分析BitTorrent是否是高效的.本文有以下贡献:①提出一种有效度量BitTorrent式的内容分发协议的方法.②确认BitTorrent的Choking/Unchoking机制存在缺陷,不是高效的.③设计ShareStorm协议,证明BitTorrent的缺陷可以避免.经初步验证,在下载完成时间这个最主要的性能指标上,ShareStorm比BitTbrrent至少减少50 %.     

多糖/石墨烯生物材料的研究应用进展

组织工程(Tissue engineering)是基于生命科学与工程学原理与技术制作生物材料用于修复、维护和促进人体各种组织或器官损伤后的功能的一门新兴学科。文章介绍了组织工程的生物材料的发展,讨论了用于加强生物材料机械强度的石墨烯的制作,综述了多糖/石墨烯分散复合物和多糖/石墨烯共价官能化制作生物材料的研究应用进展。新的多糖-官能化石墨烯的发展,为生物材料开拓了更加广阔的应用前景。     

氚标记(+)与(-)棉酚在大鼠主要脏器的亚细胞分布及共价结合

给大鼠腹腔及睾内注射氚标记的(+)与(-)棉酚后第7、18天,对主要脏器中各亚细胞组分的总放射活性及共价结合的放射活性进行了动态观察。结果表明,(-)棉酚在心肌线粒体共价结合放射活性较明显高于(+)棉酚;(+)及(-)棉酚在睾丸细胞膜、微粒体共价结合的放射活性随时间增高,且(-)棉酚较为明显。     

氚标记( )与(-)棉酚在大鼠主要脏器的亚细胞分布及共价结合

给大鼠腹腔及睾内注射氚标记的( )与(-)棉酚后第7、18天,对主要脏器中各亚细胞组分的总放射活性及共价结合的放射活性进行了动态观察。结果表明,(-)棉酚在心肌线粒体共价结合放射活性较明显高于( )棉酚;( )及(-)棉酚在睾丸细胞膜、微粒体共价结合的放射活性随时间增高,且(-)棉酚较为明显。     

整合蛋白连接激酶：抗肿瘤药物作用的新靶点

整合蛋白连接激酶（integrin-linked kinase,ILK)是一个Ser/Thr蛋白激酶。它能介导细胞与胸外基质的相互作用，并通过下游底物蛋白激酶B和糖原合成酶激酶3将胞外信号向下游传递。从而增强细胞的侵袭能力、促进细胞周期循环的进行并抑制细胞凋亡。一些蛋白磷酸酶如PTEN和ILKAP能够对ILK的活性或其信号传导途径进行抑制，一些小分子的ILK拮抗剂也能抑制ILK的活性。抑制ILK可使细胞恶生度和成瘤能力下降，导致细胞凋亡和G1到S期细胞周期循环的停滞。这些结果显示，抑制ILK的活性将对某些肿瘤的治疗有着非常重要的意义。近来一些研究显示，某些非甾体抗炎药、神经节苷酯在体内的作用位点就是ILK或其介导的相关途径。     

Nuclear targeting and nuclear retention of anthracycline-formaldehyde conjugates implicates DNA covalent bonding in the cytotoxic mechanism of anthracyclines.

The anthracycline, antitumor drugs doxorubicin (DOX), daunorubicin (DAU), and epidoxorubicin (EPI) catalyze production of formaldehyde through induction of oxidative stress. The formaldehyde then mediates covalent bonding of the drugs to DNA. Synthetic formaldehyde conjugates of DOX, DAU, and EPI, denoted Doxoform (DOXF), Daunoform (DAUF), and Epidoxoform (EPIF), exhibit enhanced toxicity to anthracycline-sensitive and -resistant tumor cells. Uptake and retention of parent anthracycline antitumor drugs (DOX, DAU, and EPI) relative to those of their formaldehyde conjugates (DOXF, DAUF, and EPIF) were assessed by flow cytometry in both drug-sensitive MCF-7 cells and drug-resistant MCF-7/ADR cells. The MCF-7 cells took up more than twice as much drug as the MCF-7/ADR cells, and both cell lines took up substantially more of the formaldehyde conjugates than the parent drugs. Both MCF-7 and MCF-7/ADR cells retained fluorophore from DOXF, DAUF, and EPIF hours after drug removal, while both cell lines almost completely expelled DOX, DAU, and EPI within 1 h. Longer treatment with DOX, DAU, and EPI resulted in modest drug retention in MCF-7 cells following drug removal but poor retention of DOX, DAU, and EPI in MCF-7/ADR cells. Fluorescence microscopy showed that the formaldehyde conjugates targeted the nuclei of both sensitive and resistant cells, and remained in the nucleus hours after drug removal. Experiments in which [(3)H]Doxoform was used, synthesized from doxorubicin and [(3)H]formaldehyde, also indicated that Doxoform targeted the nucleus. Elevated levels of (3)H were observed in DNA isolated from [(3)H]Doxoform-treated MCF-7 and MCF-7/ADR cells relative to controls. The results implicate drug-DNA covalent bonding in the tumor cell toxicity mechanism of these anthracyclines.     

Analysis of protein covalent modification by xenobiotics using a covert oxidatively activated tag: raloxifene proof-of-principle study

Numerous xenobiotics, including therapeutics agents, are substrates for bioactivation to electrophilic reactive intermediates that may covalently modify biomolecules. Selective estrogen receptor modulators (SERMs) are in clinical use for long-term therapy of postmenopausal syndromes and chemoprevention and provide a potential alternative for hormone replacement therapy (HRT). Raloxifene, in common with many SERMs and other xenobiotics, is a polyaromatic phenol that has been shown to be metabolically bioactivated to electrophilic and redox active quinoids. Nucleic acid and glutathione adduct formation have been reported, but little is known about protein covalent modification. A novel COATag (covert oxidatively activated tag) was synthesized in which raloxifene was linked to biotin. The COATag was reactive toward a model protein, human glutathione-S-transferase P1-1, in the presence but not the absence of monooxygenase. The covalent modification of proteins in rat liver microsomal incubations was NADPH-dependent implicating cytochrome P450 oxidase. The COATag facilitated isolation and identification of covalently modified microsomal proteins: cytosolic glucose regulated protein (GRP78/BiP), three protein disulfide isomerases, and microsomal glutathione S-transferase 1. Oxidative metabolism of raloxifene produces reactive intermediates of sufficient lifetimes to covalently modify proteins in tissue microsomes, behavior anticipated for other polyaromatic phenol xenobiotics that can be tested by the COATag methodology. The combined use of a COATag with a simple biotin-linked electrophile (such as an iodoacetamide tag) is a new technique that allows quantification of protein covalent modification via alkylation vs oxidation in response to xenobiotic reactive intermediates. The identification of modified proteins is important for defining pathways that might lead alternatively to either cytotoxicity or cytoprotection.     

Hepatoprotection by dimethyl sulfoxide. III. Role of inhibition of the bioactivation and covalent bonding of chloroform

Dimethyl sulfoxide (DMSO) has previously been shown to have the ability to attenuate chloroform (CHCl(3))-induced liver injury in the naive rat even when administered 24 h after the toxicant. These studies were undertaken to determine if the protective action by late administration of DMSO is due to an inhibition of the bioactivation of CHCl(3). This was done by comparing the cytochrome P450 inhibitors, diallyl sulfide (DAS), and aminobenzotriazole (ABT) to DMSO for their protective efficacy when administered 24 h after CHCl(3) exposure. In addition, (14)CHCl(3) was utilized to measure the effect of DMSO and ABT on the covalent binding of CHCl(3) in the liver following their late administration. Male Sprague-Dawley rats (300-350 g) received 0.75 ml/kg CHCl(3) po. Twenty-four hours later, they received ip injection of 2 ml/kg DMSO, 100 mg/kg DAS, or 30 mg/kg ABT. Plasma ALT activities and quantitation of liver injury by light microscopy at 48 h after CHCl(3) dosing indicated that all three treatments were equally effective at protecting the liver. A detailed study of the time course of injury development indicated that the protective action of DMSO was occurring within 10 h of its administration. Therefore, in the radiolabel studies, rats were killed 24-34 h after receiving 0.75 ml/kg CHCl(3) (30 microCi/kg (14)CHCl(3)) po. Treatment with ABT at 24 h after (14)CHCl(3) dosing decreased the covalent binding of (14)C to hepatic protein by 35% and reduced the amount of (14)C in the blood by 50% by 10 h after its administration. DMSO treatment did not significantly affect any of these parameters. The lack of effect by late administration of DMSO on the covalent binding of CHCl(3) would indicate that DMSO may offer protection by mechanisms other than inhibition of the bioactivation of CHCl(3). These studies also indicate that specific cytochrome P450 inhibitors may be of benefit in clinical situations to help treat the delayed onset hepatitis that can result following poisoning with an organohalogen, even if the antidotes are administered a number of hours after the initial exposure.     

Enantioselective covalent binding of 2-phenylpropionic Acid to protein in vitro in rat hepatocytes

A series of studies was conducted to investigate the potential of (R)- and (S)-2-phenylpropionic acid (2-PPA) to undergo enantioselective covalent binding to protein in freshly isolated rat hepatocytes and to determine whether such covalent binding is dependent on acyl glucuronidation or acyl-CoA formation of 2-PPA. Hepatocytes were incubated with (R,S)-, (R)-, or (S)-[1,2-(14)C(2)]-2-PPA (1 mM), and aliquots of the incubation mixture analyzed for covalent binding, acyl glucuronidation, and acyl-CoA formation over a 3 h period. Covalent binding of 2-PPA to hepatocyte protein was shown to be time-dependent and to be 4.5-fold greater for the (R)-isomer than the (S)-isomer after 3 h of incubation. The enantioselectivity of covalent binding correlated with the enantioselectivity of acyl-CoA formation (R/S = 7.0), but not with acyl glucuronidation (R/S = 0.67) of (R)- and (S)-2-PPA isomers during the 3 h incubation. Inhibition experiments were performed with (R,S)-[1,2-(14)C(2)]-2-PPA (1 mM) incubated with hepatocytes in the presence or absence of trimethylacetic acid (2 mM) or (-)-borneol (1 mM) for the inhibition of 2-PPA-CoA formation and 2-PPA acyl glucuronidation, respectively. Covalent binding of 2-PPA to hepatocyte protein exhibited a 53% decrease in cells treated with trimethylacetic acid, where a 66% decrease in 2-PPA-CoA formation occurred. Conversely, treatment with (-)-borneol, which completely inhibited 2-PPA acyl glucuronidation, only decreased covalent binding by 18.7%. These results indicate that metabolism of 2-PPA by acyl-CoA formation leads to the generation of reactive acylating CoA-thioester species that can contribute to protein covalent binding in a manner that is more extensive than the respective acyl glucuronides.     

On the mechanism of covalent binding of butylated hydroxytoluene to microsomal protein

The structures of cysteine conjugates of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) and the binding sites of BHT metabolites on microsomal protein were investigated by 13C nuclear magnetic resonance (13C-NMR) and gas-liquid chromatography/mass spectrometry. The cysteine conjugates of 2,6-di-tert-butyl-4-hydroxymethylphenol (BHT-alcohol) and 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone (quinone methide), which are metabolites of BHT found in rat liver and specifically reacts with thiol compounds, were prepared as alcoholic aqueous solutions. The molecular structure of the cysteine conjugate of BHT-alcohol agreed completely with that of quinone methide in 13C-NMR spectra or mass spectra. These spectra of both conjugates further showed that the conjugates are due to thioether binding between the 4-methyl group of metabolites and the sulfhydryl group of cysteine. When [14C]BHT-bound microsomes prepared in vitro were enzymatically hydrolyzed with Pronase E, the major radioactive material that eluted with methanol from a column of Amberlite XAD-2 and gave a positive ninhydrin reaction was identified as a cysteine conjugate of BHT by comparing its Rf values on TLC and mass spectrum. On the basis of the results, it was apparent that the binding site of activated substituents of BHT on protein was mainly the sulfhydryl group of cysteine residue.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin: covalent binding of reactive metabolic intermediates principally to protein in vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is metabolized by the mouse liver cytochrome P-450-mediated monooxygenase system to reactive intermediates which bind 'covalently' to cellular macromolecules. Although very difficult to quantitate, the presumably covalent binding to microsomal protein occurs between 120 and 2,640 times more readily than binding to deproteinized DNA in the in vitro reaction. Because of the extremely high rate of binding to protein rather than to DNA, it is visualized that TCDD metabolites may be so reactive that they bind in or near the P-450-active site where the TCDD is monoxygenated. This extreme reactivity may preclude the formation of detectable quantities of phenols, dihydrodiols, or conjugated products. The rate of TCDD metabolism is estimated to be between 9,000 and 36,000 times lower than the rate of P-450-mediated benzo[a]pyrene metabolism. To our knowledge, this is the first demonstration that TCDD is metabolized in any organism. There remains the possibility, however unlikely, that this covalently-bound radioactivity represents metabolites of contaminants--present in the radiolabeled TCDD sample in very minute amounts--rather than metabolites of tritiated TCDD itself. The possible relationship between P-450-mediated metabolism of this environmental contaminant and its extreme toxicity or teratogenicity is discussed.     

A review of the electrophilic reaction chemistry involved in covalent protein binding relevant to toxicity

Several pieces of legislation have led to an increased interest in the use of in silico methods, specifically the formation of chemical categories for the assessment of toxicological endpoints. For a number of endpoints, this requires a detailed knowledge of the electrophilic reaction chemistry that governs the ability of an exogenous chemical to form a covalent adduct. Historically, this chemistry has been defined as compilations of structural alerts without documenting the associated electrophilic chemistry mechanisms. To address this, this article has reviewed the literature defining the structural alerts associated with covalent protein binding and detailed the associated electrophilic reaction chemistry. This information is useful to both toxicologists and regulators when using the chemical category approach to fill data gaps for endpoints involving covalent protein binding. The structural alerts and associated electrophilic reaction chemistry outlined in this review have been incorporated into the OECD (Q)SAR Toolbox, a freely available software tool designed to fill data gaps in a regulatory environment without the need for further animal testing.     

The microsomal metabolism of hexachlorobenzene. Origin of the covalent binding to protein

The microsomal metabolism of hexachlorobenzene is studied, with special attention to the covalent binding to protein. The metabolites formed are pentachlorophenol and tetrachlorohydroquinone. In addition, a considerable amount of covalent binding to protein is detected (250 pmoles pentachlorophenol, 17 pmoles tetrachlorohydroquinone and 11 pmoles covalent binding in an incubation containing 50 mumoles of hexachlorobenzene). In order to establish the potential role of reductive dechlorination in the covalent binding, the anaerobic metabolism of hexachlorobenzene was investigated. At low oxygen concentrations no pentachlorobenzene was detected, and only very small amounts of pentachlorophenol as well as covalent binding, indicating a relationship between covalent binding and the microsomal oxidation of hexachlorobenzene. Incubations with 14C-pentachlorophenol at low concentrations showed that a conversion-dependent covalent binding occurs to the extent of 75 pmole binding per nmole pentachlorophenol. This is almost enough to account for the amount of label bound to protein observed in hexachlorobenzene incubations. This indicates that less than 10% of the covalent binding occurs during conversion of hexachlorobenzene to pentachlorophenol, and the remainder is produced during conversion of hexachlorobenzene to pentachlorophenol, and the remainder is produced during conversion of pentachlorophenol. The major product of microsomal oxidation of pentachlorophenol is tetrachlorohydroquinone, which is in redox-equilibrium with the corresponding semiquinone and quinone (chloranil). The covalent binding is inhibited by addition of ascorbic acid or glutathione to the hexachlorobenzene incubations. Ascorbic acid decreases the covalent binding with a simultaneous increase in formation of tetrachlorohydroquinone, probably due to a shift in the redox-equilibrium to the reduced side. Glutathione does not act as a reducing agent, since the inhibition of covalent binding is not accompanied by an increase in tetrachlorohydroquinone formation. Instead, glutathione reacts with chloranil, producing at least three stable products, probably in a Michael-type reaction. These results strongly indicate the involvement of chloranil or the semiquinone radical in the covalent binding during microsomal hexachlorobenzene metabolism.     

A review of the electrophilic reaction chemistry involved in covalent protein binding relevant to toxicity

Several pieces of legislation have led to an increased interest in the use of in silico methods, specifically the formation of chemical categories for the assessment of toxicological endpoints. For a number of endpoints, this requires a detailed knowledge of the electrophilic reaction chemistry that governs the ability of an exogenous chemical to form a covalent adduct. Historically, this chemistry has been defined as compilations of structural alerts without documenting the associated electrophilic chemistry mechanisms. To address this, this article has reviewed the literature defining the structural alerts associated with covalent protein binding and detailed the associated electrophilic reaction chemistry. This information is useful to both toxicologists and regulators when using the chemical category approach to fill data gaps for endpoints involving covalent protein binding. The structural alerts and associated electrophilic reaction chemistry outlined in this review have been incorporated into the OECD (Q)SAR Toolbox, a freely available software tool designed to fill data gaps in a regulatory environment without the need for further animal testing.     

A semi-automated method for measuring the potential for protein covalent binding in drug discovery

INTRODUCTION: Covalent protein binding of metabolically reactive intermediates of drugs has been implicated in drug toxicity including the occurrence of idiosyncratic drug toxicity. Investigators therefore would prefer to avoid developing compounds that produce significant amounts of reactive metabolites. By incubating the radiolabeled drug of interest with liver microsomes it is possible to evaluate the propensity of a drug candidate to covalently bind to proteins. METHODS: Here we present a semi-automated method in which a Brandel cell harvester is used to collect and wash proteins that have been incubated with radiolabeled drug. This method utilizes glass fiber filter paper to capture precipitated protein, rather than the more traditional exhaustive extraction/centrifugation approach. Using model compounds (including [14C]diclofenac, [3H]imipramine, [14C]naphthalene, and [14C]L-746530) we compare the covalent binding results obtained using this method to results generated using the traditional method and we performed cross-laboratory testing of assay reproducibility. RESULTS: It was found that results from new method correlated highly with the traditional method (R2=0.89). The cross-laboratory testing of the method showed an average interlaboratory coefficient of variation of only 18.4%. DISCUSSION: This method provides comparable results to the more traditional centrifugation-based method with considerable time and labor savings.