X-ray Studies of Sugar-Modifying Enzymes

核苷酸连接的糖存在于所有生物体中，它们发挥着各种重要的生物学作用。在半乳糖代谢中，这个实验室12年来一直关注的主要焦点之一，糖附着在UDP上。有趣的是，许多脱氧糖具有广泛的生物活性，从介导细胞间相互作用到作为各种抗生素的成分，它们是通过α - d -葡萄糖-1磷酸附着在CDP或TDP上的生化途径合成的。这项拨款更新的总体目标是通过x射线晶体学和定点诱变技术了解特异性修饰核苷酸连接糖的酶的结构。将被研究的系统包括来自假结核杆菌IVA的人udp -半乳糖4- epimase， CDP-D-tyvelose 2- epimase，来自S. fradiae的2,3-d4水解酶，以及从委内瑞拉S.分离的7种参与去糖胺生物合成的酶。udp -半乳糖4-外甲酰基酶通过催化udp -半乳糖和udp -葡萄糖的相互转化，在半乳糖代谢中起作用。CDP-tyvelose。Tyvelose存在于某些革兰氏阴性细菌的o抗原中。这些2,3-脱水酶催化了肌糖生物合成的第一步。肌糖和去糖胺都是脱氧糖，存在于一些大环内酯类抗生素中，如红霉素。udp -半乳糖4-聚二聚体酶的研究已进入最后阶段。关于脱氧糖生物合成的酶的研究是全新的。最终，新的结构分析将产生蛋白质与配体相互作用的详细三维描述，并可能最终为设计新的抗菌剂提供分子基础。

Nucleotide-linked sugars are found in all organisms where they fulfill a variety of important biological roles. In galactose metabolism, which has been one of the main focuses of this laboratory for twelve years, the sugar is attached to UDP. Interestingly, many of the deoxysugars, which display wide ranges of biological activities from mediating cell-cell interactions to serving as components in various antibiotics, are synthesized via biochemical pathways starting with the attachment of alpha-D-glucose-1 phosphate to either CDP or TDP. The overall goal of this grant renewal is to understand by x-ray crystallographic and site-directed mutagenesis techniques, the structures of enzymes that specific modify nucleotide-linked sugars. The systems that will be investigated include human UDP-galactose 4-epimerase, CDP-D-tyvelose 2-epimerase from Y. pseudotuberculosis IVA, 2,3-d4ehydratase from S. fradiae, and seven enzymes isolated from S. venezuelae that are involved in the biosynthesis of desosamine. UDP-galactose 4-epimerase functions in galactose metabolism by catalyzing the interconversion of UDP-galactose and UDP-glucose. CDP-tyvelose. Tyvelose occurs in the O-antigens of some types of gram-negative bacteria. These 2,3-dehydratase to be studied catalyzes the first step in mycarose biosynthesis. Both mycarose and desosamine are deoxysugars found in some macrolide antibiotics such as erythromycin. The research on UDP-galactose 4-epimerase is in its final stage. The proposed studies on enzymes involved deoxysugars biosynthesis are completely new. Ultimately new structural analysis will yield detailed three-dimensional descriptions of protein: ligand interactions and may eventually provide a molecular foundation upon which to base the design of new antimicrobial agents.