Structure and function of family 1 glycosyltransferases

描述（由申请人提供）：NDP-糖糖基转移酶对于所有复杂碳水化合物和糖缀合物的生物合成至关重要。这类酶催化糖单元转移到目标化合物上，以在植物、动物和细菌中产生各种大分子：糖脂、脂多糖、植物中的聚糖结构、糖蛋白和具有生物医学重要性的糖基化天然产物，如抗生素、激素、抗肿瘤剂和强心苷。最初，我们打算确定3个亚家族的家庭1 NDP-糖基转移酶（GTF）的X射线晶体结构：GTF参与万古霉素组抗生素的生物合成，GTF创造甾醇葡萄糖苷，和两个GTF参与二酰基甘油的糖基化。我们的目标是阐明（1）识别NDP-糖的物理基础，（2）识别糖苷配基受体的物理基础，和（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。更好地理解次级代谢产物的糖基化也将为针对病原生物的抗生素设计和其他生物医学相关化合物的设计（例如，强心苷或抗肿瘤剂）。家族1 NDP-糖糖基转移酶在跨物种的同源酶之间以及在物种内的类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保守性水平非常低（通常<25%同一性）。最近的研究还发现了结构同源性的不同元素，这些元素在这一功能类别的所有成员之间都是保守的。通过比较蛋白质序列分析，家族1酶的结构数据库可以允许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-糖糖基转移酶的相对简单的双结构域设计提高了设计具有新功能的嵌合酶的可能性。将混合酶设计与组合生物合成相结合可以提供生产具有生物医学重要性的新型糖缀合物的实用方法。

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.