植物凝集素的功能

植物凝集素是来源于植物的一类能凝集细胞和沉淀单糖或多糖复合物的非免疫来源的非酶蛋白质。由于其对于单糖或糖复合物特异性结合的能力,使得其在如信号转导、免疫反应、植物防御等诸多信号过程中均具有重要作用。同时植物凝集素具有细胞凝集、抗病毒、抗真菌及诱导细胞凋亡或自噬等多种能力,因此在生命科学、医学及农业方面均有较好的研究价值和应用前景。综述了植物凝集素的研究历史和凝集素的主要功能,并对现阶段凝集素的重点应用做简要介绍。     

变链菌葡聚糖结合植物血凝素的研究

植物血凝素(1ectin)一词,起源于拉丁语Legere,它是非免起源的,能与糖类结合的一类蛋白质,具有使细胞凝集和多糖沉淀的性质。一般而言,植物凝集素是由二至四个亚单位的寡聚蛋白,个别植物凝集素分子的亚单位可达十八个,通常每个亚单位有一个能与糖结合的位点,这样使植物血凝素能凝能植物和动物的细胞,在含糖的微分子之间起连接作用,其连接方式主要是疏水键和氢键。不同的植物血凝素在分子量大小,氨基酸组成,对金属的需求及三维结构方面都不相同。最早的凝集素是1888在植物中发现的,所以命名为植物凝集素。当时,Stillmark在蓖麻子中发现了一种蛋白酶细胞凝集因子。至今,已分离了几百种凝集素,发现其不光存在于植物中,亦存在于动物和微生物中,几乎见于各种生活的有机体,并不限于特殊的器官和组织。     

植物凝集素类受体蛋白激酶研究进展

自然界中植物的生长发育受到各种环境变化的影响。为了响应外界各种环境条件,植物演化出一系列识别和传递环境信号的蛋白分子,其中比较典型的是植物细胞质膜上的类受体蛋白激酶(RLKs)。凝集素类受体蛋白激酶(LecRLKs)是类受体蛋白激酶家族中的一个亚族,它主要包含3个结构域:细胞外凝集素结构域、跨膜结构域和细胞内激酶结构域。根据细胞外凝集素结构域的不同, LecRLKs可分为3种不同类型:L、G和C型。近年来,研究表明LecRLKs在植物生物/非生物胁迫和发育调控中发挥非常重要的作用。该文综述了植物凝集素类受体蛋白激酶的研究历史、结构特点、分类以及生物学功能,并重点阐述凝集素类受体蛋白激酶在植物生物/非生物胁迫响应和调控发育方面的功能。对不同类型和不同功能的植物凝集素类受体蛋白激酶进行阐述将有利于对该类蛋白开展功能研究,并为作物改良提供有益借鉴。     

植物凝集素类受体蛋白激酶研究进展

自然界中植物的生长发育受到各种环境变化的影响。为了响应外界各种环境条件,植物演化出一系列识别和传递环境信号的蛋白分子,其中比较典型的是植物细胞质膜上的类受体蛋白激酶(RLKs)。凝集素类受体蛋白激酶(LecRLKs)是类受体蛋白激酶家族中的一个亚族,它主要包含3个结构域:细胞外凝集素结构域、跨膜结构域和细胞内激酶结构域。根据细胞外凝集素结构域的不同,LecRLKs可分为3种不同类型:L、G和C型。近年来,研究表明LecRLKs在植物生物/非生物胁迫和发育调控中发挥非常重要的作用。该文综述了植物凝集素类受体蛋白激酶的研究历史、结构特点、分类以及生物学功能,并重点阐述凝集素类受体蛋白激酶在植物生物/非生物胁迫响应和调控发育方面的功能。对不同类型和不同功能的植物凝集素类受体蛋白激酶进行阐述将有利于对该类蛋白开展功能研究,并为作物改良提供有益借鉴。     

植物凝集素的分子生物学研究

植物凝集素是一类具有高度特异性糖结合活性的蛋白,含有一个或多个可与单糖或寡聚糖特异可逆结合的非催化结构域。它的糖结合特异性主要针对外源寡糖,主要生理功能是介异植物的防御反应。到目前为止已克隆了２２２个植物凝集素基因。作者就植物凝集素的分类、性质、功能、凝集素基因的克隆和凝集素的翻译后加工过程作一综述。     

豆科凝集素研究进展

豆科凝集素是植物凝集素中最丰富,也是研究最多的一类凝集素。在生理条件下豆科凝集素大多是以二聚体或四聚体的形式存在,这种低聚物的形式给予豆科凝集素较强的糖专一性和大分子结构的稳定性。豆科凝集素除作为植物储存物质的作用外,还具有识别糖蛋白、糖肽及生物膜中碳水化合物和作为植物与微生物的共生介质等生理功能。现对豆科凝集素的结构、功能及其在生物学、农业和医学方面的应用进行了综述。     

芝麻凝集素的纯化及其性质

凝集素作为研究细胞表面糖蛋白的结构和功能的探针,日益引起人们的兴趣。各种来源的凝集素可以有不同的糖结合专一性,这就为研究含糖高分子中糖部分的结构提供了一个有效的手段。我们在从各科植物种子中筛选凝集素时发现,芝麻抽提液含有能与多糖结合的蛋白     

中国水仙凝集素基因NTA的克隆、序列分析及蛋白结构预测

凝集素是一种糖专一性结合蛋白,它可以识别不同的糖类.植物凝集素是植物防御系统重要的组成部分.本研究采用RT-PCR的方法,从中国水仙花蕾中克隆了凝集素基因NTA,运用生物信息学方法对其核苷酸序列、编码的氨基酸序列进行分析以及对其蛋白结构进行预测.结果表明,得到的NTA基因全长698 bp,包含一个完整的开放阅读框516bp.该基因编码一个含有172个氨基酸的凝集素前体蛋白,该前体蛋白的等电点和分子量分别为5.84和18 615.19 Da.序列比对结果表明该基因编码的蛋白与其他单子叶植物如杂种水仙、雪花莲、君子兰、石蒜花和孤挺花的凝集素蛋白的同源性较高,分别为84%、80%、77%、78%以及82%.蛋白结构预测表明,中国水仙凝集素蛋白与洋水仙凝集素蛋白在结构上非常相似.对该基因编码的蛋白进行分析及蛋白结构模拟可知,该蛋白含有三个特殊的功能结构域和alpha-D卜甘露糖结合表面(QXDXNXVXY).     

新的豆类凝集素FRIL及其体外维持造血干/祖细胞特性的作用机制

凝集素是一类蛋白质或糖蛋白。自然界中,很多植物可产生凝集素。植物凝集素在分子间的识别过程中起着重要作用。本文主要就新近发现的豆类凝集素FRIL的生物学特性及体外维持造血干／祖细胞的作用机制进行综述。     

植物凝集素类受体激酶参与非生物胁迫响应的研究进展

植物在生长发育过程中会受到各种胁迫因子的影响,非生物胁迫是其中极其重要的一类。类受体激酶(receptor-like kinases, RLKs)是植物中广泛存在的一类蛋白,能够快速有效地对胁迫因子作出响应,最终引起一系列生物效应。凝集素类受体激酶(lectin receptor-like kinases, LecRLKs)是RLKs的一个亚族,其具有细胞外凝集素结构域、跨膜结构域和细胞内激酶结构域三个结构域。根据细胞外凝集素结构域的不同可分为L、G和C三种不同类型。近年来,大量的研究表明植物凝集素类受体激酶在非生物胁迫响应中发挥重要作用。LecRLKs通过识别非生物胁迫相关的信号分子,激活下游的信号通路,如MAPK通路、ROS通路、钙信号通路等,调节基因表达和蛋白质翻译以增强植物的抗逆性。该文概述了植物凝集素类受体激酶的结构特征及其分类,并系统综述了LecRLKs在盐胁迫、低温胁迫、干旱胁迫、机械损伤和植物激素等非生物胁迫响应中的功能和作用机制,同时也对LecRLKs的未来研究方向作出了展望。该文不仅为深入了解植物凝集素类受体激酶参与非生物胁迫响应的功能提供了参考,而且为利用LecRLKs进行作物抗逆育种改良提供了理论依据。     

植物凝集素及其在抗虫植物基因工程中的应用

植物凝集素是一类具有特异糖结合活性的蛋白,具有一个或多个可以与糖或寡聚糖特异可逆结合的非催化结构域。其糖结合活性是针对外源寡糖,参与植物的防御反应。本文综述了有关植物凝集素分子生物学的研究进展,介绍了植物凝集素的分类、糖结合特性、近年来有关植物凝集素蛋白晶体结构的研究,及其与糖结合能力相关的生物学功能。并对植物凝集素在抗虫植物基因工程中的应用现状及发展前景做了阐述。 Abstract:Plant lectins are proteins possessing at least one non-catalytic domain that binds reversibly to specific mono-or oligosaccharides.They distinguish themselves from other plant proteins by the ability of carbohydrate binding.Most plant lectins are directed to bind foreign polysacchride.Plant lectin is believed to take part in the defense responses against invader.In this paper we presented a review on the classification,characters,functions,crystal structure and,functions related to the carbohydrate binding activity.The status and prospect of plant lectins utilization were also discussed.     

A database analysis of jacalin-like lectins: sequence-structure-function relationships

Lectins are known to be important for many biological processes, due to their ability to recognize cell surface carbohydrates with high specificity. Plant lectins have been model systems to study protein-carbohydrate recognition, because individually they exhibit high sensitivity and as a group large diversity in recognizing carbohydrate structures. Although extensive studies have been carried out for legume lectins that have led to interesting insights into the sequence determinants of sugar recognition in them, frameworks with such specific correlations are not available for other plant lectin families. This study reports a large-scale data acquisition and extensive analysis of sequences and structures of beta-prism-I or jacalin-related lectins (JRLs) and shows that hypervariability in the binding site loops generates carbohydrate recognition diversity, a strategy analogous to that in legume lectins. Analyses of the size, conformation, and sequence variability in key regions reveal the existence of a common theme, encoded as a set of structural features over a common scaffold, in defining specificity. This study also points to the remarkable range of domain architectures, often arising out of gene duplication events in lectins of this family. The data analyzed here also indicate a spectacular variety of quaternary associations possible in this family of lectins that have implications for glycan recognition. These results thus provide sequence-structure-function correlations, an understanding of the molecular basis of carbohydrate recognition by beta-prism-I lectins, and also a rationale for engineering specific recognition capabilities in relevant molecules.     

Plant lectins,from ancient sugar‐binding proteins to emerging anti‐cancer drugs in apoptosis and autophagy

Ubiquitously distributed in different plant species, plant lectins are highly diverse carbohydrate‐binding proteins of non‐immune origin. They have interesting pharmacological activities and currently are of great interest to thousands of people working on biomedical research in cancer‐related problems. It has been widely accepted that plant lectins affect both apoptosis and autophagy by modulating representative signalling pathways involved in Bcl‐2 family, caspase family, p53, PI3K/Akt, ERK, BNIP3, Ras‐Raf and ATG families, in cancer. Plant lectins may have a role as potential new anti‐tumour agents in cancer drug discovery. Thus, here we summarize these findings on pathway‐ involved plant lectins, to provide a comprehensive perspective for further elucidating their potential role as novel anti‐cancer drugs, with respect to both apoptosis and autophagy in cancer pathogenesis, and future therapy.     

Crystal structure of banana lectin reveals a novel second sugar binding site

Banana lectin (Banlec) is a dimeric plant lectin from the jacalin-related lectin family. Banlec belongs to a subgroup of this family that binds to glucose/mannose, but is unique in recognizing internal alpha1,3 linkages as well as beta1,3 linkages at the reducing termini. Here we present the crystal structures of Banlec alone and with laminaribiose (LAM) (Glcbeta1, 3Glc) and Xyl-beta1,3-Man-alpha-O-Methyl. The structure of Banlec has a beta-prism-I fold, similar to other family members, but differs from them in its mode of sugar binding. The reducing unit of the sugar is inserted into the binding site causing the second saccharide unit to be placed in the opposite orientation compared with the other ligand-bound structures of family members. More importantly, our structures reveal the presence of a second sugar binding site that has not been previously reported in the literature. The residues involved in the second site are common to other lectins in this family, potentially signaling a new group of mannose-specific jacalin-related lectins (mJRL) with two sugar binding sites.     

The first crystal structure of a Mimosoideae lectin reveals a novel quaternary arrangement of a widespread domain

The crystal structures of the apo and mannose-bound Parkia platycephala seed lectin represent the first structure of a Mimosoideae lectin and a novel circular arrangement of beta-prism domains, and highlight the adaptability of the beta-prism fold as a building block in the evolution of plant lectins. The P.platycephala lectin is a dimer both in solution and in the crystals. Mannose binding to each of the three homologous carbohydrate-recognition domains of the lectin occurs through different modes, and restrains the flexibility of surface-exposed loops and residues involved in carbohydrate recognition. The planar array of carbohydrate-binding sites on the rim of the toroid-shaped structure of the P.platycephala lectin dimer immediately suggests a mechanism to promote multivalent interactions leading to cross-linking of carbohydrate ligands as part of the host strategy against phytopredators and pathogens. The cyclic structure of the P.platycephala lectin points to the convergent evolution of a structural principle for the construction of lectins involved in host defense or in attacking other organisms.     

Plant‐insect interactions: what can we learn from plant lectins?

Many plant lectins have high anti‐insect potential. Although the effects of most lectins are only moderately influencing development or population growth of the insect, some lectins have strong insecticidal properties. In addition, some studies report a deterrent activity towards feeding and oviposition behavior. Transmission of plant lectins to the next trophic level has been investigated for several tritrophic interactions. Effects of lectins with different sugar specificities can vary substantially with the insect species under investigation and with the experimental setup. Lectin binding in the insect is an essential step in exerting a toxic effect. Attempts have been made to study the interactions of lectins in several insect tissues and to identify lectin‐binding receptors. Ingested lectins generally bind to parts of the insect gut. Furthermore, some lectins such as the Galanthus nivalus agglutinin (GNA) cross the gut epithelium into the hemolymph and other tissues. Recently, several candidate lectin‐binding receptors have been isolated from midgut extracts. To date little is known about the exact mechanism for insecticidal activity of plant lectins. However, insect glycobiology is an emerging research field and the recent technological advances in the analysis of lectin carbohydrate specificities and insect glycobiology will certainly lead to new insights in the interactions between plant lectins and insects, and to a better understanding of the molecular mechanisms involved. © 2010 Wiley Periodicals, Inc.     

High-resolution structure of a new Tn antigen-binding lectin from Vatairea macrocarpa and a comparative analysis of Tn-binding legume lectins

Plant lectins have been studied as histological markers and promising antineoplastic molecules for a long time, and structural characterization of different lectins bound to specific cancer epitopes has been carried out successfully. The crystal structures of Vatairea macrocarpa (VML) seed lectin in complex with GalNAc-α-O-Ser (Tn antigen) and GalNAc have been determined at the resolution of 1.4 Å and 1.7 Å, respectively. Molecular docking analysis of this new structure and other Tn-binding legume lectins to O-mucin fragments differently decorated with this antigen provides a comparative binding profile among these proteins, stressing that subtle alterations that may not influence monosaccharide binding can, nonetheless, directly impact the ability of these lectins to recognize naturally occurring antigens. In addition to the specific biological effects of VML, the structural and binding similarities between it and other lectins commonly used as histological markers (e.g., VVLB4 and SBA) strongly suggest VML as a candidate tool for cancer research.     

从生物大分子结构特征解析植物凝集素的多样性

利用计算机模拟分析了植物凝集素结构与功能的特征。结果显示：(1)植物凝集素在结合糖之前其结构变化是一致的;(2)植物凝集素存在结构上的多样性,且可能与其生物功能的多样性有关;(3)在结合糖的过程中,植物凝集素表面局部结构的构象会有所变化,这种变化有利于其识别不同的糖而结合不同的外来糖缀合物,发挥其防御功能。对于同一家族的植物凝集素,虽然序列同源性较高,但在功能上却表现出强烈的多样性。分析表明：对于生物大分子而言,欲完成同一功能,不一定结构相同;结构相同,不一定功能一样。     

Structural basis of oligomannose recognition by the Pterocarpus angolensis seed lectin

The crystal structure of a Man/Glc-specific lectin from the seeds of the bloodwood tree (Pterocarpus angolensis), a leguminous plant from central Africa, has been determined in complex with mannose and five manno-oligosaccharides. The lectin contains a classical mannose-specificity loop, but its metal-binding loop resembles that of lectins of unrelated specificity from Ulex europaeus and Maackia amurensis. As a consequence, the interactions with mannose in the primary binding site are conserved, but details of carbohydrate-binding outside the primary binding site differ from those seen in the equivalent carbohydrate complexes of concanavalin A. These observations explain the differences in their respective fine specificity profiles for oligomannoses. While Man(alpha1-3)Man and Man(alpha1-3)[Man(alpha1-6)]Man bind to PAL in low-energy conformations identical with that of ConA, Man(alpha1-6)Man is required to adopt a different conformation. Man(alpha1-2)Man can bind only in a single binding mode, in sharp contrast to ConA, which creates a higher affinity for this disaccharide by allowing two binding modes.