Development of HBsAg-Binding Aptamers that bind HepG2.2.15 cells via HBV surface antigen

Hepatitis B virus surface antigen(HBsAg),a specific antigen on the membrane of Hepatitis B virus (HBV)-infected cells,provides a perfect target for therapeutic drugs.The development of reagents with high affinity and specificity to the HBsAg is of great significance to the early-stage diagnosis and treatment of HBV infection.Herein,we report the selection of RNA aptamers that can specifically bind to HBsAg protein and HBsAg-positive hepatocytes.One high affinity aptamer,HBs-A22,was isolated from an initial ...     

灭活铜绿假单胞菌适体的筛选

利用指数富集配基的系统进化(SELEX)技术,以灭活的铜绿假单胞菌为靶标,从体外合成的96 nt随机ssDNA文库中筛选与铜绿假单胞菌特异结合的适体.在第12轮和第14轮与其它假单胞菌属进行反筛策略,并进行了适体的结合亲和力的测定,再分别利用ClustalX、Mega2和Mfold sever软件分析适体的一级和二级结构.研究结果表明,经过15轮筛选,随机ssDNA文库与铜绿假单胞菌结合的A值从0.022上升到0.448.反筛与未反筛的结合A比值最高比为53倍.经过第15轮反筛后的24个阳性克隆子测序,根据软件分析,其可分成10个家族.每个家族都有其共同的保守序列（除第10个家族）,其中有2条序列几乎完全一致(F23和F47),同源性达到97%,A值分别高达1.598和1.508,Kd为14.55和77.46 nmol/L,间接说明适体与铜绿假单胞菌的结合力明显增高.     

核酸适配体在肿瘤免疫治疗中的应用

核酸适配体是指通过指数富集的配体系统进化技术(systematic evolution of ligands by exponential enrichment, SELEX)技术得到的一种可以高特异性、高亲和性识别靶标物质的单链DNA或RNA,可以作为靶向性治疗的分子探针。指数富集的配体系统进化技术即SELEX技术是在体外合成一个随机序列的文库,通过4个步骤孵育、分离、回收、扩增即可获得相对应的核酸适配体。通过几十年的发展,如今SELEX技术已成为一种重要的研究手段。核酸适配体具有稳定性强、分子量小、易进行化学合成和修饰、能特异性结合包括从小分子到细胞等靶标,识别范围广等优点,被广泛应用在肿瘤领域。免疫治疗与传统的肿瘤治疗方式不同,它是增强机体自身免疫系统来达到清除体内肿瘤细胞的一种方式,已被临床证明是治疗多种癌症的有效方法,例如针对免疫检查点CTLA4和PD-L1/PD-1的抗体,临床试验取得了成功,这为肿瘤的治疗带来了新的思路方法。目前,相关的免疫治疗药物已经上市应用于临床治疗,但是通过免疫治疗获益的肿瘤患者相对较少且会产生严重的副作用。核酸适配体与免疫相结合,为肿瘤的治疗提供了...     

基于适体技术的桔青毒素检测方法的建立

桔青毒素（citrinin,CTN）是以玉米、谷物、奶酪等为主要成分的食品和动物饲料中常见的、由桔青霉菌产生的酮类真菌毒素,可引起人和动物的慢性中毒或癌症,一直缺少灵敏的快速检测方法。本文通过指数富集适体系统进化技术（简称SELEX）对可能与CTN结合的特异性适体进行了筛选,经过15轮循环,得到17条适体。通过二级结构分析、亲和力检测发现适体13（Apt-13）对CTN有较好的亲和度,解离常数Kd为0.06μmol/L。进一步利用非荧光标记染料PicoGreen,利用其与双链DNA结合的原理,建立了桔青毒素非标记荧光检测方法,30min完成检测,最低检测限达到国家标准（50ppb）且与其他毒素无交叉反应。本研究建立的基于适体的桔青毒素检测技术成本低,可以替代传统的基于抗体的检测方法,为霉菌毒素的精准检测技术的开发提供了实验证据。     

RNA适体研究及其在医药上的应用

核酸适体（nucleic acid aptamer）是从人工合成的随机单链核酸库中筛选出的特异性与靶物质高度亲和的核酸分子,包括DNA适体和RNA适体. 体外获得核酸适体的方法称为指数富集配体系统进化技术,即SELEX（systematic evolution of ligands by exponential enrichment）. 在SELEX技术获得的核酸适体中,RNA适体因其结构的多样性而具有靶分子广、亲和力高、特异性强等特点. 同时,相比传统抗体,RNA适体分子量小、易改造修饰、制备方便且无免疫原性. 因此,RNA适体在基础研究、临床诊断、药物研制等方面展现了广阔的应用前景. 本文综述了RNA适体的产生、特点、作用方式、优势与局限性,并详细介绍了其在医药研究领域的应用.     

A screening method for DNA aptamers that bind to␣a␣specific, unidentified protein in tissue samples

Aptamers are oligonucleotide ligands with a high affinity to, and specificity for, various target molecules and they are expected to be powerful tools for proteomic analysis. To select aptamers that bind to a specific unidentified protein in tissues for protein analysis, a screening method was developed using chicken skeletal muscle as a model. Target proteins in the target mixture were separated by electrophoresis and transferred to a membrane, and a DNA library was added onto it. The aptamers that bound to the target protein were visualized by chemiluminescence and collected by cutting out the visualized band. The specific aptamers to the target protein were selected by only one round of selection using this screening, suggesting this screening method might be useful for selecting aptamers for proteome analysis.     

Analysis of the evolution of the thrombin-inhibiting DNA aptamers using a genetic algorithm

We previously identified a thrombin-inhibiting DNA aptamer that was presumed to form a G-quartet structure with a duplex. To investigate the importance of the sequences in the duplex region and to obtain aptamers with higher inhibitory activities, we randomized the sequences of the duplex region of this aptamer and carried out selection based on inhibitory activity using a genetic algorithm. This method consisted of selection via an inhibition assay, crossover, and mutation in silico. After two cycles, we obtained ligands with greater inhibitory activities than that of the original aptamer. In addition, the duplex sequences were found to contribute to the inhibitory activities of aptamers.     

Production of Guanosine by Psicofuranine and Decoyinine Resistant Mutants of Bacillus subtilis

Growth of Bacillus subtilis AG169 that produced large amounts of xanthosine and guanosine was inhibited by psicofuranine. When AG169 was mutated to resistance against psicofuranine, a mutant, GP–1, which yielded more guanosine was obtained. Psicofuranine did not inhibit growth of GP–1 any more. The guanosine 5′-monophosphate (GMP) synthetase activities were then assayed. In GP–1, the specific activity decreased about half, the complete loss of repression by GMP was found, and the inhibition by GMP was slightly loosed, when compared with those of AG169.

Furthermore, as growth of GP–1 was strongly inhibited by decoyinine, decoyinine resistant mutants were derived from GP–1. Of these mutants, two strains, MG–1 and MG–4, were resistant to decoyinine completely and showed the exclusive accumulation of guanosine in high yields, i.e. 16.0 and 15.5 g of guanosine per liter with weight yields of 20.0 and 19.4% of consumed sugar, respectively. GMP synthetase activity of MG–1 increased remarkably in comparison with that of GP–1 or AG169, and the inhibitions by GMP, psicofuranine and decoyinine were completely released in MG–1. Namely, the psicofuranine and decoyinine resistances seemed to cause mainly variations of GMP synthetase, and as results, the conversion of xanthosine 5′-monophosphate (XMP) to GMP proceeded more smoothly, and a larger amount of guanosine was accumulated.     

核酸适配体及其在病原微生物学中的应用

核酸适配体指利用指数富集配体系统进化技术筛选出的寡聚核苷酸片段,它可以特异性地识别靶标并与之结合,已经广泛应用于基础研究、临床诊断、纳米技术等。以下综述了适配体在微生物学方面的应用。     

SELEX法筛选宫颈癌前病变核酸适配子

构建随机ssDNA文库,通过SELEX技术,以正常、炎性宫颈脱落细胞为反筛细胞,以上皮内低级别病变(CIN1)、上皮内高级别病变(CIN2、CIN3)和鳞状细胞癌脱落细胞为正筛细胞,经过12轮筛选特异性适配子高度富集得到宫颈癌前病变适配子库,经特异性、亲和力分析和细胞免疫荧光确立高特异性适配子CIN-Ap4可作为诊断宫颈癌前病变生物标志物,为宫颈癌前病变分子诊断奠定理论基础,提供新思路。利用Prime Premier 5.0设计构建了随机ssDNA文库并根据文库两端固定序列设计引物,对对称PCR和间接不对称PCR中的退火温度、循环数以及上、下游引物浓度比等条件进行优化,分析确定50μL反应体系中对称PCR的最佳反应条件为:最佳退火温度为49.5℃,最佳循环数为15个循环;间接不对称PCR的最佳反应条件为:50μL反应体系中上、下游引物浓度的最佳比例为80∶1,最佳循环数为35个循环。实验结果表明成功构建了寡核苷酸文库,在最适PCR条件下可获得理想的dsDNA和ssDNA,并具有良好的重复性,为顺利筛选适配子提供保证。     

应用双向热循环消减SELEX技术筛选胃癌血清核酸适配体

胃癌是发病率及死亡率均较高的消化道恶性肿瘤之一,严重威胁人类的生命健康。血清肿瘤标志物的检测对提高早期胃癌的检出率,改善胃癌的治疗有重要的意义。核酸适配体以其灵敏度高、靶向性强等优势显示出了较强的临床适用性。本研究以双向热循环消减指数富集式配基系统进化(systematic evolution of ligands by exponential enrichment,SELEX)技术为支持,纳米（琼脂）磁珠材料为载体,胃癌血清及正常人血清为筛选靶标,结合高通量测序技术建立了快速高效的核酸适配体筛选方法。经过19轮双向筛选,获得高重复率的胃癌血清特异性核酸适配体序列10条及正常人血清特异性核酸适配体序列8条。将这些序列分别混合并制成检测试剂A、B,结合实时荧光定量PCR（quantitative real-time PCR,qPCR）技术,对100份临床血清样本进行特异性验证。通过比较分析,建立了快速高效的胃癌血清检测技术。结果显示,核酸适配体G AP1与N AP1的二级结构类似于抗体的“Y”型,且呈茎环状。检测试剂A、B对胃癌及正常人血清的检出率分别为92%和88%。表明本技术可以较准确地筛选得到高特异性和强亲和力的核酸适配体,体现了核酸适配体作为新型肿瘤标志物在临床检测及治疗的应用潜力。     

指数富集的配体系统进化技术筛选大肠杆菌表达的人CD20胞外蛋白特异性适配体

CD20是B细胞淋巴瘤表面标志蛋白,其膜外区是特异性抗体和药物的作用靶点。为了获得靶向CD20的特异性适配体,首先根据密码子简并性对CD20胞外区基因进行优化,使之易于在大肠杆菌中表达;然后将优化后的基因克隆到pGEX-4T-1载体中,转化到大肠杆菌BL21(DE3)中表达;蛋白纯化后用SDS-PAGE和Western blotting进行鉴定;通过指数富集的配体系统进化技术(systematic evolution of ligands by exponential enrichment,SELEX)筛选出与融合蛋白特异性结合的ssDNA适配体,并用流式细胞术检测适配体与CD20的亲和力;再通过细胞毒性试验检测适配体抑制B淋巴瘤细胞的效果。本研究建立了CD20的原核表达方法,获得了特异性结合CD20胞外区蛋白的适配体,为靶向CD20的治疗药物的开发奠定了基础。     

In vitro selection of high-affinity nucleic acid ligands to parasite target molecules

The logic of using nucleic acids as pharmaceutical reagents is in part based on their capacity to interact with high affinity and specificity with other biological components. Considerable progress has been made over the past 10 years in the development of nucleic acid-based drug molecules using a variety of different technologies. One approach is a combinatorial technology that involves an iterative Darwinian-type in vitro evolution process, which has been termed SELEX for 'systematic evolution of ligands by exponential enrichment'. The procedure is a highly efficient method of identifying rare ligands from combinatorial nucleic acid libraries of very high complexity. It allows the selection of nucleic acid molecules with desired functions and it has been instrumental in the identification of a number of synthetic DNA and RNA molecules, so-called aptamers that recognise ligands of different chemical origin. The method is fast, it does not require special equipment and the selected aptamers typically bind their target with high affinity and high specificity. Here we summarise the recent examples of the SELEX technique within the context of identifying high-affinity ligands against parasite target molecules.     

BAFF蛋白特异性核酸适配体的筛选与鉴定

系统性红斑狼疮（systemic lupus erythematosus,SLE）是我国最常见的自身免疫性疾病。B细胞活化因子（B cell activating factor,BAFF）是SLE治疗和检测的重要靶标。发展针对BAFF的经济高效的新型分子识别元件具有重要意义。利用指数富集配体系统进化（systematic evolution of ligands exponential enrichment,SELEX）体外筛选技术,从78 nt的单链DNA随机文库中筛选BAFF蛋白的核酸适配体。经过10轮筛选,高通量测序分析后,采用斑点印迹、Eastern印迹、酶联寡核苷酸吸附实验（enzyme-linked oligonucleotide assay,ELONA）检测,核酸适配体Apt 7和Apt 12可特异性识别BAFF蛋白,解离常数分别为241.00±19.75 nmol/L和413.51±46.94 nmol/L。经分子对接分析,将核酸适配体Apt 7截短为Apt 7～1,解离常数为192.10±28.61 nmol/L。联合核酸适配体Apt 7～1与BAFF抗体建立夹心ELONA法检测BAFF蛋白,检测限为0.227 nmol/L。该研究为BAFF蛋白检测和拮抗剂研究提供了新的分子识别元件。     

全细菌SELEX法筛选粪肠球菌特异性适配体

肠球菌（Enterococcus）是内源性和外源性医院感染的第二大病原菌,检出率仅次于大肠杆菌,从分子水平上发展靶标的高亲和力分子探针对肠球菌的识别和检测具有非常重要的意义。本研究以粪肠球菌为靶标,运用全细菌指数富集的配体系统进化技术（whole-bacteria systematic evolution of ligands by exponential enrichment, whole-bacteria SELEX）,从全长为79个核苷酸包含35个随机碱基序列的单链DNA文库中筛选与靶标高亲和力、高特异性结合的适配体,利用荧光分析法监控筛选过程中不同轮次所得次级文库与粪肠球菌的结合力,经12轮筛选和克隆测序,获得了39条适配体序列。进一步对筛选得到的适配体进行序列比对、二级结构分析、流式细胞分析、解离常数（Kd）测定及特异性验证,最终获得一条与粪肠球菌能特异性结合的适配体Apt 21,其Kd值为549.2 ± 147.4 nmol/L。该适配体可作为粪肠球菌检测的识别元件,为建立基于适配体的新型粪肠球菌检测方法奠定了基础。     

双向热循环消减-SELEX方法筛选肝癌血清核酸适配体

肝癌位于我国肿瘤死亡率第2位,生存率较低。目前用于肝癌早期诊断的临床检查及血清肿瘤标志物检测的特异性与敏感性均较低,不能满足肝癌早期诊断和治疗的需要。核酸适配体与靶标分子结合的灵敏度高、特异性强,有巨大的临床诊断和治疗应用前景。本文利用双向热循环消减指数富集的配基系统进化（systematic evolution of ligands by exponential enrichment, SELEX）技术,分别以肝癌血清和健康人血清为靶标,经过19轮筛选,获得了肝癌血清特异性核酸适配体序列1 000余条,以及健康人血清特异性核酸适配体序列1 000余条,并从中各挑取了1条高丰度适配体序列,分别命名为Tc1和Tn1。采取了50例肝癌病人血清和50例健康人血清,对适配体Tc1和Tn1与靶标血清的结合特异性进行了检测。结果显示,Tc1和Tn1对两种靶标血清的检出率分别为92%和94%。说明Tc1可特异性与肝癌血清结合,Tn1可特异性与健康人血清结合。肝癌血清特异性核酸适配体的筛选获得,将为建立基于核酸适配体的肝癌血清检测新方法奠定基础。