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.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM054346-10
Application #
6876066
Study Section
Bio-Organic and Natural Products Chemistry Study Section (BNP)
Program Officer
Ikeda, Richard A
Project Start
1996-07-01
Project End
2008-03-31
Budget Start
2005-04-01
Budget End
2006-03-31
Support Year
10
Fiscal Year
2005
Total Cost
$332,550
Indirect Cost
Name
University of Texas Austin
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
170230239
City
Austin
State
TX
Country
United States
Zip Code
78712
Lin, Chia-I; McCarty, Reid M; Liu, Hung-wen (2013) The biosynthesis of nitrogen-, sulfur-, and high-carbon chain-containing sugars. Chem Soc Rev 42:4377-407
Choi, Sei-hyun; Mansoorabadi, Steven O; Liu, Yung-nan et al. (2012) Analysis of UDP-D-apiose/UDP-D-xylose synthase-catalyzed conversion of UDP-D-apiose phosphonate to UDP-D-xylose phosphonate: implications for a retroaldol-aldol mechanism. J Am Chem Soc 134:13946-9
Sun, He G; Ruszczycky, Mark W; Chang, Wei-Chen et al. (2012) Nucleophilic participation of reduced flavin coenzyme in mechanism of UDP-galactopyranose mutase. J Biol Chem 287:4602-8
Choi, Sei-hyun; Ruszczycky, Mark W; Zhang, Hua et al. (2011) A fluoro analogue of UDP-*-D-glucuronic acid is an inhibitor of UDP-*-D-apiose/UDP-*-D-xylose synthase. Chem Commun (Camb) 47:10130-2
Ruszczycky, Mark W; Choi, Sei-hyun; Mansoorabadi, Steven O et al. (2011) Mechanistic studies of the radical S-adenosyl-L-methionine enzyme DesII: EPR characterization of a radical intermediate generated during its catalyzed dehydrogenation of TDP-D-quinovose. J Am Chem Soc 133:7292-5
Romo, Anthony J; Liu, Hung-wen (2011) Mechanisms and structures of vitamin B(6)-dependent enzymes involved in deoxy sugar biosynthesis. Biochim Biophys Acta 1814:1534-47
Sasaki, Eita; Liu, Hung-Wen (2010) Mechanistic studies of the biosynthesis of 2-thiosugar: evidence for the formation of an enzyme-bound 2-ketohexose intermediate in BexX-catalyzed reaction. J Am Chem Soc 132:15544-6
Sasaki, Eita; Ogasawara, Yasushi; Liu, Hung-Wen (2010) A biosynthetic pathway for BE-7585A, a 2-thiosugar-containing angucycline-type natural product. J Am Chem Soc 132:7405-17
Borisova, Svetlana A; Liu, Hung-Wen (2010) Characterization of glycosyltransferase DesVII and its auxiliary partner protein DesVIII in the methymycin/picromycin biosynthetic pathway. Biochemistry 49:8071-84
Borisova, Svetlana A; Guppi, Sanjeeva R; Kim, Hak Joong et al. (2010) A de novo approach to the synthesis of glycosylated methymycin analogues with structural and stereochemical diversity. Org Lett 12:5150-3

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