Structure and function of family 1 glycosyltransferases

描述(由申请人提供)：NDP-糖基转移酶对所有复杂碳水化合物和糖共轭化合物的生物合成至关重要。这一大类和多样化的酶催化糖单元转移到目标化合物上，从而在植物、动物和细菌中产生一系列不同的大分子：糖脂、脂多糖、植物中的多糖结构、糖蛋白以及具有生物医学意义的糖基化天然产物，如抗生素、激素、抗肿瘤药物和心脏糖苷。首先，我们打算确定NDP-糖基转移酶家族1的三个亚家族的X射线晶体结构：参与万古霉素类抗生素生物合成的糖基转移酶，产生甾醇糖苷的糖基转移酶，以及参与二酰甘油糖基化的两个糖基转移酶。我们的目标是阐明(1)识别NDP-糖的物理基础，(2)识别苷元受体的物理基础，以及(3)糖基转移的机制。了解这些酶的结构多样性将增强我们对糖生物学的理解，特别是关于糖脂、糖类固醇和抗生素的生物合成。更好地了解次生代谢物的糖基化也将为针对病原体的抗生素设计和其他生物医学相关化合物的设计(例如，强心苷或抗肿瘤药物)开辟新的途径。家族1 NDP-糖基转移酶在不同物种的同源酶之间以及物种内的相似酶之间显示出显著的功能保守性，尽管在许多情况下氨基酸序列的保守性很低(通常为25%)。最近的研究还检测到在这一功能类的所有成员之间保守的结构同源性的不同元件。通过比较蛋白质序列分析，家族1酶的结构数据库可以对该家族中任何结构未知的蛋白质进行建模。此外，家族1 NDP-糖基转移酶相对简单的双域设计增加了设计具有新功能的嵌合酶的可能性。将杂交酶设计与组合生物合成相结合，可以提供实用的方法来生产具有生物医学意义的新的糖偶联物。

DESCRIPTION (provided by applicant): NDP-sugar glycosyltransferases are critical for the biosynthesis of all complex carbohydrates and glycoconjugates. This large and diverse class of enzymes catalyzes the transfer of saccharide units onto the target compounds to create a diverse set of macromolecules in plants, animals, and bacteria: glycolipids, lipopolysaccharides, the glycan structures in plants, glycoproteins, and glycosylated natural products of biomedical importance like antibiotics, hormones, antitumor agents, and cardiac glycosides. Initially, we intend to determine the X-ray crystal structures of 3 subfamilies of the family 1 NDP-sugar glycosyltransferases (GTFs): GTFs involved in the biosynthesis of vancomycin group antibiotics, GTFs which create sterol glucosides, and two GTFs involved in the glycosylation of diacylglycerol. Our goals are to elucidate (1) the physical basis for the recognition of NDP-sugars, (2) the physical basis for the recognition of the aglycone acceptors, and (3) the mechanism of glycosyltransfer. Understanding the structural diversity of these enzymes will enhance our understanding of glycobiology, particularly regarding the biosynthesis of glycolipids, glycosteroids, and antibiotics. A better understanding of the glycosylation of secondary metabolites will also open up new avenues for antibiotic design against pathogenic organisms and the design of other biomedically relevant compounds (e.g., cardiac glycosides or antitumor agents). Family 1 NDP-sugar glycosyltransferases show significant conservation of functionality among homologous enzymes across species as well as between analogous enzymes within a species, despite very low levels of amino acid sequence conservation (often <25% identity) in many cases. Recent research has also detected distinct elements of structural homology that are conserved between all members of this functional class. With comparative protein sequence analysis, a structural database of the family 1 enzyme could allow the modeling of any structurally unknown protein within this family. Moreover, the relatively simple bi-domain design of family 1 NDP-sugar glycosyltransferases raises the possibility of designing chimeric enzymes with novel functionalities. Mixing hybrid enzyme design with combinatorial biosynthesis could provide practical ways to produce new glycoconjugates of biomedical importance.