核糖体失活蛋白—RNA N—糖苷酶

本文概述了双链和单链植物核糖体失活蛋白的基本特性,在分子水平上讨论了核糖体失活蛋白作用于真核细胞核糖体的机制。扼要介绍了免疫毒素及其在癌症治疗中的应用。同时,也讨论了目前有关核糖体失活蛋白的研究状况和今后的发展趋向。     

植物核糖体失活蛋白及其应用进展

植物核糖体失活蛋白（ribosome-inactivating proteins,RIPs）是一类作用于真核细胞rRNA,并破坏其核糖体结构,抑制蛋白质生物合成的毒蛋白,主要应用在农业和医学领域。在农业领域,主要应用在转基因植物中,增强其抗病毒、抗菌以及抗虫活性。在医学领域,主用应用于抗肿瘤、抗艾滋病病毒等研究中。对核糖体失活蛋白的一些性质和应用进展进行综述。     

抗真菌蛋白研究进展

对几种抗真菌蛋白 :病程相关蛋白、防卫素、核糖体失活蛋白、几丁质连接蛋白、蛋白酶抑制剂等的类型、特征、抗菌菌机理进行了阐述 ,着重讨论了病程相关蛋白和核糖体失活蛋白的最新研究进展 ,并且讨论了抗真菌蛋白在植物真菌病害综合防治中的应用前景。     

核糖体失活蛋白的结构功能与分布

核糖体失活蛋白是一类在植物中较广泛存在的毒蛋白。植物核糖体失活蛋白具有RNAN-糖苷酶活力,可作用于核糖体RNA,使核糖体失去蛋白质合成的功能。根据一级结构,核糖体失活蛋白可分为两种类型。Ⅰ型核糖体失活蛋白由一条链组成,分子量在25—30 kDa之间。Ⅱ型核糖体失活蛋白由两条以二硫键相连的链(A、B链)组成,分子量在60 kDa左右。B链可以与细胞表面含半乳糖的受体结合,有助于A链进入细胞,作用于核糖体。目前至少已从9个科31种植物中分离纯化了Ⅰ型RIP。Ⅱ型RIP较少,仅在6科8种植物中发现。除了具有RNA N-糖苷酶活性,还发现一些核糖体失活蛋白可以切割超螺旋双链DNA,产生缺口环状和线状DNA。此外,一种Ⅰ型RIP,克木毒蛋白还具有超氧化物歧化酶活性。     

核糖体失活蛋白研究进展

核糖体失活蛋白是一类毒蛋白, 主要存在于植物当中, 在真菌和细菌中也有发现。其共同特点是具有N-糖苷酶活性, 能水解生物核糖体大亚基rRNA颈环结构上特定位点的腺嘌呤, 使核糖体失活, 从而抑制了蛋白质合成。本文对核糖体失活蛋白的主要性质、应用以及国内外有关这类蛋白的研究进展加以概述。     

植物中的核糖体失活蛋白及其抗病毒机制

植物中的核糖体失活蛋白是一类分布于植物体内的毒蛋白,其作用于真核细胞大亚基28S导致核糖体失活,抑制蛋白质的生物合成,从而对细胞产生毒害作用.文章简述了植物核糖体失活蛋白的酶活性和抗病毒的可能分子机制.     

核糖体失活蛋白研究进展

核糖体失活蛋白是一类毒蛋白,主要存在于植物当中,在真菌和细菌中也有发现.其共同特点是具有N-糖苷酶活性,能水解生物核糖体大亚基rRNA颈环结构上特定位点的腺嘌呤,使核糖体失活,从而抑制了蛋白质合成.本文对核糖体失活蛋白的主要性质、应用以及国内外有关这类蛋白的研究进展加以概述.     

核糖体单链失活蛋白在无细胞体系中的活性

核糖体单链失活蛋白是一类广泛分布于植物中的蛋白质,它能使真核细胞核糖体60S亚基失活。本文报道了一些核糖体单链失活蛋白的制备、纯化以及在兔网织红细胞裂解液中对蛋白质生物合成的抑制活性及它们对完整细胞的毒性。其中多数的核糖体单链失活蛋白是首次被分离纯化并对其毒性进行研究的。     

植物的核糖体失活蛋白及其应用

对植物的核糖体失活蛋白的分类、性质、功能和应用的研究进展作概述。     

核糖体失活蛋白及其在植物抗真菌病基因工程中的应

真菌病是农作物减产的主要原因之一。而植物界大量存在着具有离体抑制真菌生长增殖能力的蛋白质 ,核糖体失活蛋白 (RIP ,ribosomeinactivatingprotein)就是其一。它能特异地水解核糖体RNA 3′ 端茎环结构的腺嘌呤残基而导致核糖体失活 ,进而抑制蛋白合成。但它却不使自身的核糖体失活 ,只对其它物种核糖体显示高度特异性 ,这显然具有防止外来病原体侵染的功能。利用基因工程技术 ,使其在一些经济作物中高效表达 ,筛选具有抗性的转基因植株 ,这正日益成为植物真菌病防治的新途径。它克服了常规育种周期长 ,抗性种质缺乏的弊端 ,更避免了施用农药带来的环境污染等问题 ,其应用前景甚为广阔。围绕其在抗真菌病基因工程中的应用 ,本文对核糖体失活蛋白在植物体中的分布、分类、生化、结构、功能特性、作用机制以及应用前景等作简要、全面的阐述。     

Ribosome-Inactivating Proteins: A Family of Plant Proteins That Do More Than Inactivate Ribosomes

Many plants contain proteins that are commonly designated as ribosome-inactivating proteins (RIPs). Based on the structure of the genes and the mature proteins a novel system is proposed to unambiguously classify all RIPs in type-1, type-2, and type-3 RIPs. In addition, the concept of one- and two-chain type-1 RIPs is introduced. After an overview of the occurrence, molecular structure, and amino acid sequences of RIPs, the formation of the mature proteins from the primary translation products of the corresponding mRNAs is elaborated in detail in a section dealing with the biosynthesis, posttranslational modifications, topogenesis, and subcellular location of the different types of RIPs. Details about the three-dimensional structure of type-1 RIPs and the A and B chains of type-2 RIPs are discussed in a separate section. Based on the data given in the previous sections, the phylogenic and molecular evolution of RIPs is critically assessed and a novel model is proposed for the molecular evolution of RIPs. Subsequently, the enzymatic activities of RIPs are critically discussed whereby special attention is given to some presumed novel activities, and a brief overview is given of the biological activities of the different types of RIPs on cells and whole organisms. By combining the data on the enzymatic activities and biological activities of RIPs, and the current knowledge of different plant physiological aspects of these proteins, the role of RIPs in plants is revisited. Thereby the attention is focussed on the role of RIPs in plant defense with the emphasis on protection against plant-eating organisms and viruses. Finally, there is a short discussion on the discovery of a novel class of enzymes called RALyases that use ribosomes damaged by RIPs as a substrate and may act cooperatively with RIPs. There is discussion regarding why the identification of this novel enzyme gives valuable clues to the origin and original function of RIPs and may be helpful to unravel the physiological role of modem RIPs.     

Analysis of castor bean ribosome-inactivating proteins and their gene expression during seed development

Ribosome-inactivating proteins (RIPs) are enzymes that inhibit protein synthesis after depurination of a specific adenine in rRNA. The RIP family members are classified as type I RIPs that contain an RNA-N-glycosidase domain and type II RIPs that contain a lectin domain (B chain) in addition to the glycosidase domain (A chain). In this work, we identified 30 new plant RIPs and characterized 18 Ricinus communis RIPs. Phylogenetic and functional divergence analyses indicated that the emergence of type I and II RIPs probably occurred before the monocot/eudicot split. We also report the expression profiles of 18 castor bean genes, including those for ricin and agglutinin, in five seed stages as assessed by quantitative PCR. Ricin and agglutinin were the most expressed RIPs in developing seeds although eight other RIPs were also expressed. All of the RIP genes were most highly expressed in the stages in which the endosperm was fully expanded. Although the reason for the large expansion of RIP genes in castor beans remains to be established, the differential expression patterns of the type I and type II members reinforce the existence of biological functions other than defense against predators and herbivory.     

Ribosome-inactivating proteins with an emphasis on bacterial RIPs and their potential medical applications

Ribosome-inactivating proteins (RIPs) are toxic due to their N-glycosidase activity catalyzing depurination at the universally conserved α-sarcin loop of the 60S ribosomal subunit. In addition, RIPs have been shown to also have other enzymatic activities, including polynucleotide:adenosine glycosidase activity. RIPs are mainly produced by different plant species, but are additionally found in a number of bacteria, fungi, algae and some mammalian tissues. This review describes the occurrence of RIPs, with special emphasis on bacterial RIPs, including the Shiga toxin and RIP in Streptomyces coelicolor recently identified in S. coelicolor. The properties of RIPs, such as enzymatic activity and targeting specificity, and how their unique biological activity could be potentially turned into medical or agricultural tools to combat tumors, viruses and fungi, are highlighted.     

Ribosome-inactivating proteins from plants: more than RNA N-glycosidases?

Many plants contain proteins that are capable of inactivating ribosomes and accordingly are called ribosome-inactivating proteins or RIPs. These typical plant proteins receive a lot of attention in biological and biomedical research because of their unique biological activities toward animal and human cells. In addition, evidence is accumulating that some RIPs play a role in plant defense and hence can be exploited in plant protection. To understand the mode of action of RIPs and to optimize their medical and therapeutical applications and their use as antiviral compounds in plant protection, intensive efforts have been made to unravel the enzymatic activities of RIPs and provide a structural basis for these activities. Though marked progress has been made during the last decade, the enzymatic activity of RIPs has become a controversial issue because of the concept that RIPs possess, in addition to their classical RNA N-glycosidase and polynucleotide:adenosine glycosidase activity, other unrelated enzymatic activities. Moreover, the presumed novel enzymatic activities, especially those related to diverse nuclease activities, are believed to play an important role in various biological activities of RIPs. However, both the novel enzymatic activities and their presumed involvement in the biological activities of RIPs have been questioned because there is evidence that the activities observed are due to contaminating enzymes. We offer a critical review of the pros and cons of the putative novel enzymatic activities of RIPs. Based on the available data, it is suggested that there is little conclusive evidence in support of the presumed activities and that in the past too little attention has been given to the purity of the RIP preparation. The antiviral activity and mode of action of RIPs in plants are discussed in view of their classical and presumed novel enzymatic activities.     

Enzymatic activity of toxic and non-toxic type 2 ribosome-inactivating proteins

Ribosome-inactivating proteins (RIPs) display adenine polynucleotide glycosylase activity on different nucleic acid substrates, which at the ribosomal level is responsible for the arrest of protein synthesis. Some type 2 RIPs, namely ricin and related proteins, are extremely toxic to mammalian cells and animals whilst other type 2 RIPs (non-toxic type 2 RIPs) display three to four logs less toxicity. We studied whether a correlation exists between toxicity on cells and enzymatic activity on nucleic acids. All type 2 RIPs differ in their depurinating activity on the different substrates with differences of up to one to two logs. The toxicity of type 2 RIPs is independent of their enzymatic activity on nucleic acids or on ribosomes.     

Ribosome inactivating proteins and apoptosis

Ribosome inactivating proteins (RIPs) are protein toxins that are of plant or microbial origin that inhibit protein synthesis by inactivating ribosomes. Recent studies suggest that RIPs are also capable of inducing cell death by apoptosis. Though many reports are available on cell death induced by RIPs, the mechanism involved is not well studied. Comparison of pathways of apoptosis and cellular events induced by various RIPs suggests a central role played by mitochondria, probably acting as an integrator of cellular stress and cell death. The purpose of this review is to compare the various apoptotic pathways that may be involved and propose a general pathway in RIP-induced cell death.     

核糖体失活蛋白在细胞内的转运途径

核糖体失活蛋白（ribosome—inactivating proteins,RIPs）是一类抑制蛋白质生物合成的毒蛋白,现已成为研究细胞生物学的重要工具并在临床抗肿瘤和抗病毒治疗上得到了广泛应用。现结合国内外近几年的研究进展就核糖体失活蛋白在细胞内的转运途径作一综述。     

核糖体灭活蛋白在植物中的作用

植物核糖体灭活蛋白 (ribosome -inactivatingproteins ,RIPs)能够破坏真核或原核细胞的核糖体大亚基RNA ,使核糖体失活而不能与蛋白质合成过程中的延伸因子相结合 ,从而导致蛋白质合成受到抑制。不同的核糖体对不同RIPs的敏感性不同 ,RIPs对自体或异体核糖体的作用也有很大区别。RIPs对病毒有很强的抑制作用 ,并且有些RIPs表现出对某些真菌和昆虫的抗性 ,因此认为核糖体灭活蛋白在植物的防御反应中扮演重要角色。另外 ,RIPs还可能参与了细胞代谢、细胞死亡等生理调控过程。