蛋白糖基化与免疫

蛋白质糖基化是蛋白质翻译后的一种重要的加工过程，在肽链合成的同时或合成后，在酶的催化下糖链被接到肽链上的特定糖基化位点，称为蛋白质糖基化。蛋白质糖基化的种类主要有N-糖苷(N-dycan)、O-糖苷(O-glycan)、糖基磷脂酰肌醇(GPI，phosphatidyl insitol glycan)等。机体大多数糖蛋白为     

IgG糖基化修饰及其意义研究进展

蛋白糖基化修饰是特异糖链在细胞内质网中添加到蛋白质上形成寡糖链的过程,具有酶定向和位点特异性.根据与蛋白质部分连接方式的不同,蛋白质糖基化修饰分为O-连接和N-连接两种.其生物合成在内质网和高尔基体内进行,可大致分为三步[1]:(1)在内质网中形成含有3个葡萄糖、9个甘露糖和2个乙酰胺葡萄糖的寡聚糖-脂复合物,其中的脂质部分(多萜醇)起转运作用;(2) 寡糖部分转移至正在合成的多肽链,并同时移除3个葡萄糖和1个甘露糖;(3)未加工成熟的糖蛋白转移至高尔基体,加工形成(Man)5(GlcNAc)2糖链,然后再在特定糖基转移酶或糖苷酶(见表1)作用下继续加工[2-4].最终在各种不同酶的参与下形成多种长度、组成和结构各不相同的糖链.     

N-糖链参与细胞凋亡的研究进展

N-糖基化蛋白质的寡聚糖链(简称N-糖链)在参与细胞与细胞的粘附、识别以及蛋白受体调节的细胞表面蛋白中发挥着重要作用,干扰N-糖链生成途径中寡聚糖转移酶和磷酸多萜醇的结构和功能或完全阻断N-糖链的生成都会影响细胞凋亡的进程.     

空肠弯曲菌蛋白糖基化系统及利用该系统在大肠杆菌中表达糖蛋白的研究进展

蛋白质糖基化是蛋白质翻译后的一种重要加工过程,其种类主要有N-糖基化和O-糖基化.N-糖基化是指寡糖链连接在蛋白的天冬酰胺β-酰胺氮上,O-糖基化是指寡糖链连接在蛋白的丝氨酸、苏氨酸或酪氨酸的羟基的氧原子上.自从1976年在古细菌中发现S-层糖蛋白以来,已经在古细菌和细菌中发现70多种糖基化蛋白[1-2],并且大部分属于O-糖蛋白,是细菌鞭毛或纤毛的组成成分[3].人体内超过一半的蛋白质是糖基化蛋白质[4],糖基化蛋白质的糖链在机体的正常生理活动中具有重要功能和作用[5].蛋白质药物的糖基化可以增强蛋白质药物的生物活性、延长其半衰期、增加其溶解性、改善其免疫原性等,目前70%的治疗性蛋白质药物均是糖蛋白[6-7 ].生产糖蛋白的首选宿主是中国仓鼠卵巢细胞,生产效率低,成本高,部分蛋白糖链具有免疫原性;另外,毕赤酵母表达系统和昆虫细胞也可以用来生产糖蛋白,但这两种表达系统生产的糖蛋白的糖链为高甘露糖型或含有杂糖,具有较强的免疫原性.大肠杆菌表达系统是应用最广泛的经典表达系统,该系统缺乏真核细胞所特有的蛋白质翻译后的糖基化修饰过程,一直以来该系统只能表达非糖基化蛋白质.然而,近10年来发现空肠弯曲菌(Campylobacter jejuni)中存在糖蛋白,把空肠弯曲菌中存在的蛋白糖基化相关基因转化到大肠杆菌中则能够在大肠杆菌中表达带有糖链的目的蛋白.本文对空肠弯曲菌中存在的糖基化系统和利用该系统在大肠杆菌中表达带有糖链的目的蛋白的研究进展进行综述.     

蛋白质O-GlcNAc糖基化与心血管疾病

正蛋白质O连接N-乙酰葡萄糖胺糖基化(O-linkedN-acetylglucosaminylation,O-Glc NAcylation;简称OGlc NAc糖基化)是指单个N-乙酰葡萄糖胺(N-acetyl-glucosamine,Glc NAc)以O-糖苷键连接到底物蛋白质丝氨酸或苏氨酸残基上的一种蛋白质翻译后修饰。生理水平的O-Glc NAc糖基化在代谢和免疫稳态等方面具有重要作用,其水平异常则与心血管疾病、代谢综合征和癌症等疾病的发生密切相关[1-2]。     

糖基化在肿瘤免疫中的作用

正蛋白质的糖基化是糖类在糖基转移酶(Glycosyltransferase,GTs)的催化下以共价键的形式与肽链连接的过程。根据糖肽键的不同,糖基化分为以下四种类型:N-连接糖基化、O-连接糖基化、糖基磷脂酰肌醇(Glycophosphatidylinositol,GPI)锚定糖基化和C-甘露糖化[1]。蛋白质的糖基化通过影响新生肽链的空间结构,定位及稳定性,而参与到细胞识别     

非酶促蛋白糖基化及其与糖尿病并发症

蛋白质的非酶促糖基化是蛋白质翻译后的主要修饰方式之一,是糖的醛基或酮基与蛋白质分子中赖氨酸或羟赖氨酸的ε-氨基结合形成糖基化蛋白质的反应过程。由法国化学家H·M.Maillard于1912年首次发现,故又称麦拉德(Maillard)反应。非酶促糖基化蛋白在临床诊断及糖尿病合并症的发生发展中起重要作用,是糖尿病领域的重要研究课题。本文简述蛋白质非酶促糖基化的过程、影响因素、特性及生物学意义。     

新型O-连接糖基化——O-GlcNAc

一种新型糖基化,单糖N-乙酰葡糖胺通过O-连接与蛋白质共价相连。随着研究的不断深入,这种新型糖基化受到愈来愈多的重视。本文主要论述它的发现,存在部位及可能的功能。     

蛋白质糖基化病理生理的研究进展

1980年Gend和Browlee等发现糖尿病患者体内蛋白质由于持续高血糖症而被非酶促糖基化修饰，近年进一步证实：持久的高血糖会导致人体内许多结构蛋白、功能蛋白和核酸蛋白非酶糖基化，这在糖尿病慢性并发症的发生中占有重要地位，且与衰老过程密切相关［1、2」。本文就这方面的研究作一综述。（一）糖基化终产物的基本生化特性：葡萄糖及其他糖类能与蛋白质氨基以共价键相结合形成糖基化产物，此过程无需酶的参与。糖基化是一动态的连续过程，早期形成可逆的Amadori产物，通常于数周内达到平衡；Amadori产物可经脱水及分子重排，形成一系列…     

肺癌与肺良性疾病 特异血清免疫炎性蛋白质N-糖基化修饰差异

目的探索肺癌与肺良性疾病特异血清免疫炎性蛋白质N-糖基化修饰差异。方法应用非变性聚丙烯酰胺凝胶电泳(native-PAGE)从肺腺癌和慢性肺炎患者血清中分离得到一组疾病特异的血清免疫炎性蛋白质复合物(IIRPCs),经胶内酶解、石墨相氮化碳富集分离得到完整糖肽。应用高效液相色谱-串联质谱(HPLC-MS/MS)技术,结合GPSeeker数据库检索软件进行糖肽鉴定。结果共鉴定了来自12种蛋白质的89种糖肽,其中21种仅与肺良性疾病相关,38种仅与肺癌相关。89种糖肽中包括63种糖型,其中10种为肺良性疾病特有糖型,21种为肺癌特有糖型。两种疾病的特有糖型在其结构和连接位点上均存在差异。结论发现了两种疾病血清特异免疫炎性蛋白质N-糖基化修饰的差异,为糖基化修饰在慢性疾病的诊断、预后评估和分子机制等方面的研究提供了新视角。     

Reflections on the mechanical structure of the base of the skull and on the face

Using thick sections of the base of the skull and face their mechanical structure is viewed from the engineering aspect and the anatomic solutions evolved are compared with those selected by Aerospatiale engineers for the concept and development of the Airbus. It is concluded that the anterior and middle cranial fossae, together with the face, constitute an inseparable mechanical assembly each of whose component units participate in the rigidity of the others. Since this mechanical assembly must provide maximal rigidity for minimal weight, this suggests that aeronautical solutions should throw much light on the detail of construction of the skull and face. Indeed, the rigidity and lightness of the latter are obtained by means of solutions familiar in aeronautics: the reliance on thin-shelled beams with a honeycomb filling, the diploe analogous to a preconstrained composite or sandwich structure, a system of frames, struts and stiffeners, and the use of fillets at the sites of junction of struts.     

Studies on the influence of the structural modifications in the tracer on the immunoassay of progesterone

The main objective of the present study was to examine the influence of different bridges in radioiodinated tracers on the assay performance of progesterone using antibodies. Three homologous and two heterologous immunoassay systems for the measurement of progesterone in human serum are described. Using an antiserum raised against progesterone-11alpha-hemisuccinate-bovine serum albumin (BSA), assays with homologous radioligands, namely progesterone-11alpha-hemisuccinate-125I-tyrosine methyl ester (TME) and progesterone-11alpha-hemisuccinate-125I-histamine, heterologous bridge radioligand, namely progesterone-11alpha-hemiphthalate-125I-TME, and a heterologous site radioligand namely progesterone-3-(O-carboxymethyl) oxime (CMO)-125I-histamine were optimized. A homologous assay system, using antiserum raised against progesterone-3-carboxymethyl oxime-BSA and progesterone-3-CMO-125I-histamine as the radioligand was also optimized to develop a radio-immunoassay (RIA) for serum progesterone. Amongst the two homologous radioligands, viz., progesterone-11alpha-hemisuccinate-125I-histamine and the corresponding TME conjugate tracer, the former yielded a standard curve with a higher slope (-0.6) as compared to the latter (-0.5). The heterologous bridge system with progesterone-11alpha-hemiphthalate-125I-TME resulted in a more sensitive assay (slope of -0.8) than the homologous tracers, whilst the heterologous site radioligand, viz., progesterone-3-CMO-125I-histamine gave the most sensitive assay (slope of -1.2). The homologous assay with antiserum against progesterone-3-CMO-BSA and progesterone-3-CMO-125I-histamine tracer gave a standard curve having a slope of -0.97. The two antibodies developed against progesterone, viz., progesterone-11alpha-hemisuccinate-BSA and progesterone-3-CMO-BSA were characterized for their titre, sensitivity, and specificity. Considering the slope, sensitivity, cross-reactivity, and the quality of tracer, the assay system using antiserum against progesterone-11alpha-hemisuccinate-BSA and progesterone-3-CMO-125I-histamine was found to be suitable for the development of RIA for serum progesterone. The bridges used in an immunogen for production of antibodies, as well as in the preparation of tracer, have a great influence on the assay characteristics.     

Study on the interference of ticlopidine on the immune system

In-vitro and ex-vivo studies have been performed in order to investigate the possible interference of ticlopidine on different lymphocyte parameters. In vitro, ticlopidine displays a dose-dependent inhibition of both spontaneous and lectin-induced 3H-thymidine incorporation by normal lymphocytes. Moreover the highest drug concentrations also reduce the in-vitro PWM-stimulated Ig synthesis. Lymphocyte tests performed in healthy volunteers after a 10-day oral treatment (250 mg/day) show only a slight reduction of PHA- and ConA-induced proliferative responses and in-vitro PWM-stimulated Ig synthesis. The values found after treatment however remain within the normal range, excluding a clear interference of ticlopidine on the immune parameters tested. In addition the treatment does not affect the white blood cells nor the lymphocyte subset distribution identified by the monoclonal antibodies OKT3, OKT4 and OKT8.     

Experimental studies on the effect of duodenal contents on the epithelium of the esophagus

10 male BD IX rats and 15 male and female Wistar rats weighing between 250 and 300 g had an esophago-jejunostomy according to the method described by Levrat et al. (1962). Four weeks after surgery all 40 animals were sacrificed and examined macroscopically as well as histologically. All animals had deep ulcerative lesions in the lower half of the esophagus associated with hyperplasia, hyperkeratosis and akanthosis.