PRNP基因八肽重复突变研究进展

摘要 遗传性朊病毒病由编码PrP蛋白的PRNP基因突变引起,其中八肽重复区的插入或缺失突变与家族性克雅氏病（fCJD）、GSS综合症相关。PRNP基因八肽重复突变的细胞生物学、转基因动物研究对揭示遗传性朊病毒病发病机制,进而揭示朊病毒病的致病机理具有重要意义。     

幽门螺杆菌Cag致病岛hp0527基因的缺失株构建和鉴定

目的:构建幽门螺杆菌(H.pylori)Cag致病岛编码hp0527基因的突变株.为Cag致病岛致病机制及H.priori功能研究奠定基础.方法:利用基因同源重组方法将卡那霉素抗性基因(KanR)连接到PCR扩增hp0527两端区域产生的2个目的基因片段之间,构建hp0527基因缺失的自杀质粒pBlueKM40-△hp0527;将带有卡那霉素抗性标志的缺失突变载体,通过抗生素卡那霉素筛选出缺失hp0527基因的突变株,并经PCR方法鉴定后,采用野生株和突变株的幽门螺杆菌分别与胃癌上皮细胞BGC-823共培养后,分析它们对细胞毒素相关蛋白CagA转运能力的影响.结果:成功构建出幽门螺杆菌hp0527基因突变的自杀质粒,突变载体经内切酶酶切分析显示:产生的条带与设计结果完全一致;抗生素筛选并经PCR鉴定后,获得了hp0527基因缺失株;CagA蛋白转运分析表明基因hp0527缺失前后,可以导致细菌转运CagA蛋白能力的丧失.结论:成功构建出1株缺失hp0527基因的H.pylori突变株,对于阐明该基因的功能及其在H.pylori致病中的地位及作用具有重要的研究价值.     

大肠杆菌qseC基因敲除及其缺陷株生物被膜形成的研究

目的 通过Red同源重组法构建qseC基因缺失的大肠杆菌突变株,并探讨qseC基因对大肠杆菌生物被膜形成的影响.方法 PCR扩增两翼与目的基因上下游同源、含有氯霉素抗性基因片段,电击转化人大肠杆菌MC1000,在Red同源重组酶作用下,用含同源臂的氯霉素抗性片段置换目的基因qseC,并利用FLP位点专一性重组将氯霉素抗性基因删除.结晶紫染色半定量法分析qseC基因缺失株生物被膜形成能力的变化.结果 PCR及DNA测序结果表明,qseC基因已被成功敲除.在LB培养基中,qseC基因缺陷株的生长状况与亲株无明显差异.MC1000与MC1000 △qseC基因缺失株生物被膜形成能力半定量A值的结果分别为1.00±0.15和0.47±0.10.结论 成功构建大肠杆菌qseC基因缺失突变株,且qseC基因对细菌生物被膜的形成具有调控作用.     

联合利用嵌套缺失和酚筛选法构建和鉴定目的基因的缺失突变体

目的 介绍一种快捷、无突变的目的基因缺失体构建和鉴定方法.方法 用Mlu I 和 Sac I酶将GCLC/pGL3在GCLC基因与pGL3连接处切开,形成以GCLC端为3'凹端而pGL3载体端为3'凸端的线型载体.利用外切核酸酶Ⅲ从GCLC基因端(3'凹端)单向逐一切除GCLC基因上的核苷酸,并在不同的时间终止其反应以获得一系列的GCLC基因缺失体.将GCLC基因缺失体与pGL3载体自身环化构建成GCLC基因序列缺失体的pGL3报道载体.最后用酚抽提和凝胶电泳法粗略挑选出不同长度的GCLC/pGL3缺失突变体.结果 利用嵌套缺失法构建出各种长度的GCLC基因的缺失突变体,且不存在基因突变的现象.利用酚筛选法快速鉴定出29种不同长度的缺失突变体.结论 联合利用嵌套缺失和酚筛选法可以高保真而快速地构建和鉴定目的基因的缺失突变体.     

联合利用嵌套缺失和酚筛选法构建和鉴定目的基因的缺失突变体

目的 介绍一种快捷、无突变的目的基因缺失体构建和鉴定方法.方法 用Mlu I 和 Sac I酶将GCLC/pGL3在GCLC基因与pGL3连接处切开,形成以GCLC端为3＇凹端而pGL3载体端为3＇凸端的线型载体.利用外切核酸酶Ⅲ从GCLC基因端（3＇凹端）单向逐一切除GCLC基因上的核苷酸,并在不同的时间终止其反应以获得一系列的GCLC基因缺失体.将GCLC基因缺失体与pGL3载体自身环化构建成GCLC基因序列缺失体的pGL3报道载体.最后用酚抽提和凝胶电泳法粗略挑选出不同长度的GCLC/pGL3缺失突变体.结果 利用嵌套缺失法构建出各种长度的GCLC基因的缺失突变体,且不存在基因突变的现象.利用酚筛选法快速鉴定出29种不同长度的缺失突变体.结论 联合利用嵌套缺失和酚筛选法可以高保真而快速地构建和鉴定目的基因的缺失突变体.     

朊蛋白N端和C端多肽特异性抗体的制备及ELISA检测技术的研究

目的 制备朊蛋白N端和C端多肽特异性抗体，并对ELISA方法在朊病毒病检测中的应用进行研究。方法构建人朊蛋白N端和C端多肽原核表达重组质粒，分别表达纯化融合蛋白。以此为抗原制备朊蛋白N端和C端多肽特异性抗体。ELISA和Western Blot检测所制备抗体与重组和天然的PrP蛋白的免疫反应性。初步建立间接ELISA检测技术。结果 所制备的N端和C端抗体可特异性识别重组全长PrP蛋白和相应的PrP片段，无明显交叉反应。C端抗体还可有效地识别感染羊瘙痒因子263K的仓鼠脑组织中经PK消化后的prp^Se，其Western Blot反应带型与PrP单抗3174相似。5000r／min离心处理脑组织悬液可有效保留上清中PrP^Se成分而不影响ELISA检测。蛋白酶K虽经灭活处理，但可明显抑制重组和天然PrP在液相中与相应抗体的结合。间接ELISA方法可根据反应A值区分正常或感染动物样本。结论 所制备的朊蛋白N端和C端抗体具有良好的特异性，C端抗体可用于实验性朊病毒病的检测。建立的间接ELISA方法可试用于朊病毒病的初步筛查。     

重组人N端缺失MBL的原核表达及其活性研究

目的 原核表达具生物学活性的重组人N端缺失甘露聚糖结合凝集素(rhMBLΔN)蛋白.方法 应用PCR技术,从含中国人野生型MBL cDNA的质粒pGEM-MBL中扩增rhMBLΔN基因片段,插入pET43.1a载体后,转化E.coli BL21(DE3)感受态菌诱导表达rhMBLΔN蛋白.应用Ni2 -NTA琼脂糖柱纯化目的 蛋白,以SDS-PAGE、Western blot和ELISA进行鉴定.结果 从pGEM-MBL中扩增到长约620bp的DNA片段,构建的重组表达载体经Bam HI和Eco RI酶切后出现约7270bp和620bp的片段,测序结果与预期的完全一致.表达的重组蛋白纯化后,经SDS-PAGE鉴定为Mr97000的蛋白.ELISA证实,纯化蛋白能与抗重组人MBL抗体结合,具备配体结合活性并能与人甘露聚糖结合凝集素相关丝氨酸蛋白酶1、2的N端片段结合.结论 获得了可表达rhMBLΔN的菌株和具活性的rhMBΔN蛋白,为进一步研究提供了条件.     

广州市6例克雅氏病病例特征分析

目的探讨克雅氏病（CJD）的临床表现,提高对该病的诊治能力。方法收集广州市报告的CJD患者共6例,均行磁共振成像（MRI）和脑电图检查,14-3-3蛋白及PRNP基因检测。结果多为急性亚急性起病,首发症状以进行性痴呆（2例）和椎体外系症状（2例）为主。病例均无痴呆类疾病家族史和手术、脑垂体生长激素使用史。MRI检查显示,无特异性异常信号。脑电图检查结果,均出现弥漫性慢波,4例出现特征性的周期性三相波。3例14-3-3蛋白阳性,而PRNP基因序列分析均为无突变型。1例进行脑组织活检,蛋白酶K抗性朊蛋白（PK抗性PrP）阳性。结论 CJD早期临床表现不典型,脑脊液14-3-3蛋白检测和持续动态的脑电图检查可能是CJD早期诊断的特异性方法。     

朊病毒病相关细胞凋亡

朊病毒病是一组蛋白质折叠异常的蛋白质构象病,由正常朊蛋白PrPC转化为具蛋白酶抗性的异常朊蛋白PrPSc并在中枢神经系统聚集引起.其主要的病理变化为神经元的丢失,脑组织的海绵样变及神经胶质细胞增生.目前认为其神经元丢失的主要原因为凋亡及自噬等,而神经元的凋亡涉及多种因素及途径,机制较为复杂.对神经元凋亡的研究将有助于揭示朊病毒病的发病机制.     

变异链球菌luxS基因缺陷突变株生物学性状的初步观察

目的 为研究口腔主要致龋菌变异链球菌的种属间密度感应(quorum sensing)相关基因luxS对口腔生态的影响,构建此菌的luxS基因缺失突变株.方法 采用同源重组的方法,利用红霉素耐药基因erm置换变异链球菌基因组中的luxS基因,并在含抗性标记的选择性培养基上筛选出阳性克隆.初步研究该基因的缺失突变对变异链球菌在生长与生物被膜成熟分化中的作用.结果经PCR鉴定,luxS基因的置换突变位置正确,并能在体外稳定传代,突变株与野生株相比在达静止期后总菌数量上有明显差别,但在生物被膜的形成与分化上并未发现显著差异.结论 通过此研究建立了可稳定传代的变异链球菌luxS基因的缺失突变株,生长表型和生物被膜的形成与野生株无显著差异,为进一步研究此基因功能与调控机制提供了技术平台.     

Fatal Familial Insomnia and Familial Creutzfeldt-Jakob Disease: Clinical, Pathological and Molecular Features

Fatal familial insomnia (FFI) and a subtype of familial Creutzfeldt-Jakob disease (CJD¹⁷⁸) are two prion diseases that have different clinical and pathological features, the same aspartic acid to asparagine mutation (D178N) at codon 178 of the prion protein (PrP) gene, but distinct genotypes generated by the methionine-valine polymorphism at codon 129 (129M or 129V) in the mutant allele of the PrP gene. The D178N, 129M allele segregates with FFI while the D178N, 129V allele segregates with CJD¹⁷⁸. The proteinase K resistant PrP (PrP^res) isoforms present in FFI and CJD¹⁷⁸ differ in degree of glycosylation and size. Thus, the amino acid, methionine or valine, at position 129 of the mutant allele, in conjunction with D178N mutation results in significant alterations of PrP^res in FFI and CJD¹⁷⁸. The 129 polymorphic site also exerts influence through the normal allele: the course of the disease is shorter in the patients homozygous at codon 129 and other minor but consistent phenotypic differences occur between homozygous and heterozygous FFI patients. The comparative study of PrP^res distribution in FFI homozygotes and heterozygotes at codon 129 has lead to the conclusion that the phenotypic differences observed between these two FFI patient populations may be the result of different rates of conversion of normal PrP into PrP^res, at least in some brain regions.     

Disease-associated prion protein is not detectable in human systemic amyloid deposits

Cerebral and cardiac amyloid deposits have been reported after scrapie infection in transgenic mice expressing variant prion protein (PrP(C)) lacking the glycophosphatidylinositol anchor. The amyloid fibril protein in the systemic amyloid deposits was not characterized, and there is no clinical or pathological association between prion diseases and systemic amyloidosis in humans. Nevertheless, in view of the potential clinical significance of these murine observations, we tested both human amyloidotic tissues and isolated amyloid fibrils for the presence of PrP(Sc), the prion protein conformation associated with transmissible spongiform encephalopathy (TSE). We also sequenced the complete prion protein gene, PRNP, in amyloidosis patients. No specific immunohistochemical staining for PrP(Sc) was obtained in the amyloidotic cardiac and other visceral tissues of patients with different types of systemic amyloidosis. No protease-resistant prion protein, PrP(res), was detectable by Western blotting of amyloid fibrils isolated from cardiac and other systemic amyloid deposits. Only the complete normal wild-type PRNP gene sequence was identified, including the usual distribution of codon 129 polymorphisms. These reassuringly negative results do not support the idea that there is any relationship of prions or TSE with human systemic amyloidosis, including cardiac amyloid deposition.     

Expression of PrP(C) as HIS-fusion form in a baculovirus system and conversion of expressed PrP-sen to PrP-res in a cell-free system

Conversion of the PrP cellular form (PrP(C)) to the pathogenic form (PrP(Sc)) is the key step in the pathogenesis of transmissible spongiform encephalophathies. Although the mechanism of conformational conversion of PrP proteins remains uncertain, the cell-free conversion reaction and other in vitro PrP amplification tests allow it to be studied under the much quicker and simpler conditions than those of transmission bioassay in vivo. Using baculovirus expression system, wild-type hamster (HaPrP) and human PrP (HuPrP), as well as D178N mutated human PrP (HuPrPm178) were expressed in HIS-fusion form. After 35S-methionine labeling and purification with Ni-NTA agarose affinity chromatography, individual expressed PrP proteins were mixed with PrP(Sc) isolated from hamster brain tissue infected with scrapie 263K. Protease-resistant isoform was detected in the homologous HaPrP reaction, but not in the two heterologous HuPrP preparations, implying a species-specific molecular recognition between PrP(C) and PrP(Sc). HIS-tag in HIS-HaPrP seems to have little effect on the formation of protease-resistant protein in this preparation. This system proposes a simple and protein productive-enriched way for cell-free conversion of prion proteins, as the replacement of native or genetic engineering expressed sole PrP(C) from mammalian or non-mammalian sources.     

In vitro amplification and detection of variant Creutzfeldt-Jakob disease PrPSc

Variant Creutzfeldt-Jakob disease (vCJD) poses a serious risk of secondary transmission and the need to detect infectivity in asymptomatic individuals is therefore of major importance. Following infection, it is assumed that minute amounts of disease-associated prion protein (PrP(Sc)) replicate by conversion of the host cellular prion protein (PrP(C)). Therefore, methods of rapidly reproducing this conversion process in vitro would be valuable tools in the development of such tests. We show that one such technique, protein misfolding cyclic amplification (PMCA), can amplify vCJD PrP(Sc) from human brain tissue, and that the degree of amplification is dependent upon the substrate PRNP codon 129 polymorphism. Both human platelets and transgenic mouse brain are shown to be suitable alternative substrate sources, and amplified PrP(Sc) can be detected using a conformation-dependent immunoassay (CDI), allowing the detection of putative proteinase K sensitive forms of PrP(Sc).     

Creutzfeldt-Jakob disease (CJD) with a mutation at codon 148 of prion protein gene: relationship with sporadic CJD

Creutzfeldt-Jakob disease (CJD), the most common human prion disease, includes sporadic (s) and familial (f) forms. Regardless of etiology, both forms are thought to share the pathogenic mechanism whereby the cellular prion protein (PrP(C)) converts into its pathogenic isoform (PrP(Sc)). While PrP(C) conversion is thought to be random in sCJD, conversion in fCJD is facilitated by the congenital presence of mutated PrP. Differences in PrP genotype (PRNP) and in conversion circumstances lead to PrP(Sc) with distinct characteristics that elicit different disease phenotypes. Here, we describe a case of fCJD with a substitution of histidine (H) for arginine (R) at codon 148 (R148H) and heterozygosity of the methionine/valine (M/V) polymorphic codon 129, with the 129M allele coupled with the mutation. The disease phenotype and all major characteristics of PrP(Sc) of fCJD(R148H) were virtually indistinguishable from those of sCJDMV2, which has features different from those of any other sCJD. Therefore, despite the differences in etiology, PRNP, and conversion process, the two forms of PrP(Sc) had similar characteristics. Furthermore, comparison of fCJD(R148H) with a recently reported case carrying R148H and homozygosity at codon 129 suggests that codon 129 coupled with the mutation as well as that located on the normal allele can modify major phenotypic and PrP(Sc) features of fCJD(R148H).     

两种分泌抗PrP单克隆抗体杂交瘤细胞株的建立及其初步鉴定

目的 制备具有广谱种属反应性的PrP单克隆抗体(McAb)，用于可传播性海绵样脑病(TSE)的诊断及致病机制研究。方法 分别将对应于牛PrP29-48(BoP1)、PrP89-108(BoP2)的两种多肽与匙孔碱血蓝蛋白(KLH)偶联，免疫BALB／c小鼠，经细胞融合后获得分泌针对上述两种多肽的杂交瘤细胞株，用Western-blot方法检测这些细胞株分泌的McAb与牛(Bo)、人(Hu)和仓鼠(Ha)PrP蛋白的反应性。结果 通过细胞融合和2-3轮克隆化，用ELISA筛选出分泌抗BoPl和BoP2抗体的杂交瘤细胞株D11和D8。Western blot显示，获得的McAb均能分别与重组BoPrP(25-242)、重组HuPrP(23-231)和HaPrP(23-231)反应。结论 获得了可与牛、人和仓鼠PrP反应的两种McAb，可用于哺乳类PrP检测及TSE致病机制研究。     

PRNP allelic series from 19 years of prion protein gene sequencing at the MRC Prion Unit

Mutation of the human prion protein gene (PRNP) open reading frame (ORF) accounts for almost all reported familial concurrence of prion disease. The more common mutations globally: octapeptide repeat insertions, P102L, D178N, E200K, and V210I have occurred in large multigenerational pedigrees and display autosomal dominant inheritance, however, many rare genetic changes have been reported that are of uncertain pathogenicity. Based on 19 years of PRNP sequencing at the MRC Prion Unit, London, and analysis of 3664 samples from patients referred with suspected prion disease and healthy populations, we present novel allele combinations, healthy control population data, results of screening the PRNP ORF in DNA from the entire referral series and the CEPH human genome diversity cell line panel. Of the 10 alleles detected in patients for which detailed cases histories are presented, 4 are unreported (G54S, D167N, V209M, Q212PP), two changes are thought to be pathogenic but have not been described in our regions (P105L from the UK, G114V from India and Turkey), and the remainder reported in healthy control populations or in trans to known pathogenic mutations suggesting non‐ or low pathogenicity (G54S, 1‐OPRI, G142S, N171S, V209M, E219K). New genotype‐phenotype correlations and population frequencies presented will help the diagnosis and genetic counselling of those with suspected inherited prion disease. © 2010 Wiley‐Liss, Inc.     

Molecular Pathology of Fatal Familial Insomnia

Fatal familial insomnia (FFI) is linked to a mutation at codon 178 of the prion protein gene, coupled with the methionine codon at position 129, the site of a methionine/valine polymorphism. The D178N mutation coupled with the 129 valine codon is linked to a subtype of Creutzfeldt-Jakob disease (CJD¹⁷⁸) with a different phenotype. Two protease resistant fragments of the pathogenic PrP (PrP^res), which differ in molecular mass, are associated with FFI and CJD¹⁷⁸, respectively, suggesting that the two PrP^res have different conformations and hence they produce different disease phenotypes. FFI transmission experiments, which show that the endogenous PrP^res recovered in affected syngenic mice specifically replicates the molecular mass of the FFI PrP^res inoculated and is associated with a phenotype distinct from that of the CJD¹⁷⁸ inoculated mice, support this idea. The second distinctive feature of the FFI PrP^res is the underrepresentation of the unglycosylated PrP^resform. Cell models indicate that the underrepresentation of this PrP^res form results from the PrP dys-metabolism caused by the D178N mutation and not from the preferential conversion of the glycosylated forms. Codon 129 on the normal allele further modifies the FFI phenotype determining patient subpopulations of 129 homozygotes and heterozygotes: disease duration is generally shorter, insomnia more severe and histopathology more restricted to the thalamus in the homozygotes than in the heterozygotes The allelic origin of PrP^res fails to explain this finding since in both cases FFI PrP^res is expressed only by the mutant allele. Despite remarkable advances, many issues remain unsolved precluding full understanding of the FFI pathogenesis.     

Prion Protein Amyloidosis

The prion protein (PrP) plays an essential role in the pathogenesis of a group of sporadic, genetically determined and infectious fatal degenerative diseases, referred to as "prion diseases", affecting the central nervous system of humans and other mammals. The cellular PrP is encoded by a single copy gene, highly conserved across mammalian species. In prion diseases, PrP undergoes conformational changes involving a shift from α-helix to β-sheet structure. This conversion is important for PrP amyloidogenesis, which occurs to the highest degree in the genetically determined Gerstmann-Sträussler-Scheinker disease (GSS) and prion protein cerebral amyloid angiopathy (PrP-CAA), while it is less frequently seen in other prion diseases. GSS and PrP-CAA are associated with point mutations of the prion protein gene ( PRNP ); these conditions show a broad spectrum of clinical presentation, the main signs being ataxia, spastic paraparesis, extrapyramidal signs and dementia. In GSS, parenchyma! amyloid may be associated with spongiform changes or neurofibrillary lesions; in PrP-CAA, vascular amyloid is associated with neurofibrillary lesions. A major component of the amyloid fibrils in the two diseases is a 7 kDa peptide, spanning residues 81–150 of PrP.     

Polymorphisms of SPRN (shadow of prion protein homology) in three breeds of sheep in China

The key point, which is related to the susceptibility of prion diseases in animals, has been proved to be the prion protein gene (PRNP). However, animals, especially sheep and goats, with the same PRNP genotype are not equally susceptible to the diseases. The finding of SPRN (shadow of prion protein homology) provides a new aspect to understand the diseases as protein of SPRN (Shadoo) has similar neuroprotective function and conserved hydrophobic core with prion protein (PrP). Researchers have made some efforts to demonstrate the relationship between SPRN and PRNP. Stewart’s work has shown that SPRN contained an alanine-rich sequence, which is homologous to a hydrophobic core with amyloidgenic characteristics in PrP. Here our work shows that the sheep of Inner Mongolia in China have several haplotypes with the similar results of Stewart and Daude’s. However we find a new haplotype in a Sunite sheep, which is not reported by others.