液体发酵树舌提取凝集素的生理学功能检测

本文对树舌菌丝体的深层发酵工艺进行了初步的研究。试验结果表明,树舌菌丝体在大豆培养基中培养5天,产出的总蛋白、总糖含量较高。从发酵液中分离和纯化出树舌凝集素具有明显的生物学活性。     

苦参凝集素的色氨酸残基修饰与荧光光谱研究

苦参凝集素（SFL）经等电聚焦测得其等电点为5.56,用比色法测得每分子SFL含有3个色氨酸残基,经N-溴代丁二酰亚胺（NBS）修饰表明其中2个Trp残基位于分子表面,当这2个Trp残基补修饰后,SFL的凝血活性完全丧失,糖保护试验表明,SFL专一性抑制糖Man能够保护SFL,阻断NBS对SFL的修饰作用,说明色氨酸不仅是SFL凝血活性所必需的,而且还参与其糖结合部位的组成,SFL随着NBS的逐渐修饰,其内源荧光光谱亦相应发生变化,结果表明分子表面的2个Trp残基可能位于分子的疏水袋中,而另一个Trp残基则埋藏于分子内部,荧光淬灭研究表明,丙烯酰胺能淬灭87%色氨酸残基的荧光。     

韭菜凝集素的纯化及部分性质的研究

用葡聚糖凝胶柱层析法从韭菜的叶片组织分离出一种对新鲜兔红细胞有强烈凝集作用的凝集素，ＰＡＧＥ鉴定和高碘酸－Ｓｃｈｉｆｆ试剂反应均显单一条带。ＳＤＳ－ＰＡＧＥ分析表明该凝集素含有３个亚基，其相对分子质量分别约为３１０００、２４０００和２１０００。韭菜凝集素具有一定的热稳定性，在酸、碱处理中该凝集素对碱处理较酸处理稳定，氨基酸组成分析表明韭菜凝集素含有１４种氨基酸，其中半胱氨酸含量较高。     

凝集素的分离纯化、基因克隆及功能研究进展

凝集素(lectin)研究近年来发展迅速,尤其在植物基因工程中,植物外源凝集素基因越来越受到重视。本文从凝集素的分离纯化、基因克隆、理化性质和功能等方面进行了综述。此外还讨论了凝集素基因在植物基因工程中的应用。     

白芸豆凝集素的分子稳定性和光谱性质研究

经缓冲液抽提、CM-Sepharose、DEAE-Sepharose离子交换及Sephacryl S-200分子筛层析,从白芸豆种子纯化得到白芸豆凝集素(Phaseolus coccineus lectin,PCL)。SDS-PAGE和Sephacryl S-200凝胶过滤分析表明白芸豆凝集素是由两个30 kDa的单体组成的分子量约为56 kDa的同源二聚体蛋白。凝血活性结果表明白芸豆凝集素能凝集的兔血细胞和人ABO血型细胞,无血型专一性。其凝血活性在80 ℃以下和pH 3.0-10.0时保持稳定。脲、盐酸胍对PCL凝血活性的影响表明,随着变性剂浓度的升高,凝血活性逐渐丧失。不同温度、pH和不同浓度变性剂条件下PCL的荧光光谱分析表明PCL变性过程的阶段性。     

小鼠表皮发育期间蓖麻凝集素受体的定位

采用酶标凝集素技术，在光镜水平对小鼠表皮发育期间蓖麻凝集素的受体进行定位，结果表明；在胚胎期间周皮细胞和角质层以及基膜中均有Ｇａｌ残基分布；在表皮中间层，毛根原基处无Ｇａｌ，在眼睑和眼睑缘处也无Ｇａｌ分布，Ｇａｌ可能参与表皮的角质化和基膜组建，与周皮在胚胎期发挥正常功能有关。     

Sialic acid-specific lectins: occurrence, specificity and function

Sialic acids consist of a family of acidic ninecarbon sugars that are typically located at the terminal positions of a variety of glycoconjugates. Naturally occurring sialic acids show an immense diversity of structure, and this reflects their involvement in a variety of biologically important processes. One such process involves the direct participation of sialic acids in recognition events through specific interactions with lectins, a family of proteins that recognise and bind sugars. This review will present a detailed overview of our current knowledge regarding the occurrence, specificity and function of sialic acid-specific lectins, particularly those that occur in viruses, bacteria and non-vertebrate eukaryotes. Received 13 December 2005; received after revision 9 February 2006; accepted 15 February 2006     

Role of <Emphasis Type="Italic">N</Emphasis>-linked polymannose oligosaccharides in targeting glycoproteins for endoplasmic reticulum-associated degradation

Misfolded or incompletely assembled multisubunit glycoproteins undergo endoplasmic reticulum-associated degradation (ERAD) regulated in large measure by their N-linked polymannose oligosaccharides. In this quality control system lectin interaction with Glc₃Man₉GlcNAc₂ glycans after trimming with endoplasmic reticulum (ER) -glucosidases and -mannosidases sorts out persistently unfolded glycoproteins for N-deglycosylation and proteolytic degradation. Monoglucosylated (Glc₁Man₉GlcNAc₂) glycoproteins take part in the calnexin/calreticulin glucosylation-deglucosylation cycle, while the Man₈GlcNAc₂ isomer B product of ER mannosidase I interacts with EDEM. Proteasomal degradation requires retrotranslocation into the cytosol through a Sec61 channel and deglycosylation by peptide: N-glycosidase (PNGase); in alternate models both PNGase and proteasomes may be either free in the cytosol or ER membrane-imbedded/attached. Numerous proteins appear to undergo nonproteasomal degradation in which deglycosylation and proteolysis take place in the ER lumen. The released free oligosaccharides (OS) are transported to the cytosol as OS-GlcNAc₂ along with similar components produced by the hydrolytic action of the oligosaccharyltransferase, where they together with OS from the proteasomal pathway are trimmed to Man₅GlcNAc₁ by the action of cytosolic endo--N-acetylglucosaminidase and -mannosidase before entering the lysosomes. Some misfolded glycoproteins can recycle between the ER, intermediate and Golgi compartments, where they are further processed before ERAD. Moreover, properly folded glycoproteins with mannose-trimmed glycans can be deglucosylated in the Golgi by endomannosidase, thereby releasing calreticulin and permitting formation of complex OS. A number of regulatory controls have been described, including the glucosidase-glucosyltransferase shuttle, which controls the level of Glc₃Man₉GlcNAc₂-P-P-Dol, and the unfolded protein response, which enhances synthesis of components of the quality control system.Received 26 January 2004; accepted 25 February 2004     

Glycoconjugates in sperm function and gamete interactions: how much sugar does it take to sweet-talk the egg?

Glycoconjugates in the mammalian reproductive tract are critical components of the molecular mechanisms that control sperm maturation, sperm transport and gamete interactions. In the oviduct of many species, sperm transport and maturation are regulated by protein-carbohydrate interactions that form a sperm reservoir. Subsequently, gamete interactions are mediated by the binding of lectin-like sperm proteins with carbohydrate moieties on the zona pellucida. The sperm glycocalyx is extensively modified during sperm transport and maturation. Multiple functions have been proposed for this dense carbohydrate layer overlying the sperm plasmalemma, and sperm-surface carbohydrates have been implicated in immune-mediated human infertility. The structure and function of glycoconjugates in the oviductal sperm reservoir, the zona pellucida, and on the sperm surface are reviewed.