C-C & C-N Bond Formation in Unusual Sugar Biosynthesis

描述（由申请人提供）：支链糖和含氮糖是两类重要的天然碳水化合物。这些糖作为许多生物活性天然产物的功效和特异性的重要组成部分的建立，表明通过利用其生物合成机制来改变和/或交换这些关键的糖结构可能会增强或改变其母体分子的生理特性。要充分实现这种方法的潜力，需要对每个目标糖的生物合成途径有透彻的了解，包括遗传、酶和机制信息。通过本基金资助的工作，我们朝着这些目标所做的努力取得了一些显著的成果。在上一个资助期内，我们研究了具有代表性的支链糖——mycarose、yerisose和半乳糖呋喃糖，以及两种氨基糖——mycaminose和去糖胺的形成。我们还通过探索通过操纵糖生物合成机制来改变大环内酯抗生素中附加糖来产生新的糖缀合物的可行性，扩展了该项目的范围。通过这些研究，我们现在确定了三个值得在下一个资助期进一步深入研究的领域。本提案概述了我们的计划：(A)研究tdp -二氢链糖合成酶催化形成二氢步糖的机制，(B)研究一种不寻常的硝基糖kijanose的生物合成，以及(C)利用糖基转移酶在生物合成应用中的催化能力。前两个项目的预期目标是建立kijanose生物合成的整个途径，并表征C-C和C-N键形成步骤的机制，这些步骤涉及到二氢链糖和kijanose的形成。这些研究不仅有助于描述化学转化如何受到相关酶的影响，而且还将促进未来治疗设计的努力，以控制和/或模仿它们的催化作用。从第三个项目中获得的见解将允许合理设计杂交糖缀合物，通过适当的糖基转移酶催化所需的糖与各种糖酰子的偶联，利用两种组分提供的结构多样性。这种组合方法有望探索新的化学实体，最终用于对抗对人类健康的无数微生物威胁。总的来说，我们的结果有望对酶化学的基础知识做出重大贡献，并可能影响制药生物技术。

DESCRIPTION (provided by applicant): Branched-chain sugars and nitrogen-containing sugars are two important classes of naturally occurring carbohydrates. The establishment of these sugars as vital components for the efficacy and specificity of many biologically active natural products has purported the idea that altering and/or exchanging these crucial sugar structures by exploiting their biosynthetic machineries may enhance or vary the physiological characteristics of their parent molecules. Fully realizing the potential of such an approach requires a thorough understanding of the biosynthetic pathway of each target sugar, including genetic, enzymatic, and mechanistic information. Efforts directed toward these goals have achieved some notable results through our work funded by this grant. In the last grant period, we studied the formation of representative branched-chain sugars -- mycarose, yersiniose and galactofuranose, and two amino sugars -- mycaminose, and desosamine. We also extended the scope of this project by exploring the feasibility of generating new glycoconjugates by manipulating the sugar biosynthetic machineries to alter the appended sugars in macrolide antibiotics. As a result of these studies, we have now identified three areas worthy of further in-depth investigation in the next grant period. Outlined in this proposal are our plans (A) to study the mechanism of the formation of dihydrosteptose catalyzed by TDP-dihydrostreptose synthase, (B) to investigate the biosynthesis of an unusual nitrosugar, kijanose, and (C) to exploit the catalytic capabilities of glycosyltransferases in biosynthetic applications. The intended goals of the first two projects are to establish the entire pathway for the biosynthesis of kijanose and to characterize the mechanisms of the C-C and C-N bond formation steps involved the formation of dihydrostreptose and kijanose. These studies will not only aid in delineating how chemical transformations are affected by the responsible enzymes, but will also facilitate future therapeutic design efforts to control and/or mimic their catalytic roles. The insight gained from the third project will allow rational design of hybrid glycoconjugates through the coupling of desired sugars with various aglycons catalyzed by the appropriate glycosyltransferases, harnessing the structural diversity provided by both components. Such a combinatorial approach holds promise for the exploration of new chemical entities that will ultimately be used to battle innumerable microbial threats to human health. Overall, our results are expected to make a significant contribution to the fundamentals of enzyme chemistry and possibly impact pharmaceutical biotechnology.