Synthesis and function of novel bacterial carbohydrates

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The glycome represents an extra layer of information above the genome, transcriptome and proteome and deciphering its role is a fundamental question. This question is particularly important in bacteria that produce a wide variety of glycans of heterogeneous composition. Elucidating their biosynthesis will allow assessing their function and harnessing the potential of novel sugar synthesis enzymes for biotechnology applications. We focused on modified heptoses from Campylobacters or Yersiniae and characterized 9 heptose modification enzymes that affect the function of the capsule and lipopolysaccharide in which the modified heptoses reside. Our work showed that heptose modifying reductases and epimerases from C. jejuni have very precise substrate and product specificities.*** The current proposal focuses on understanding the molecular basis of such specificity, and on elucidating the function of new methyltransferases and oxidases in heptose modification. Our work also highlighted a novel putative regulator within the C. jejuni capsular cluster, and also suggests co-regulation of capsule synthesis with the synthesis of other glycans. Elucidating the mechanisms involved may allow to better delineate the physiological role of each pathway and understand how they are integrated under physiological conditions.*** We hypothesize that: (i) the reductases and epimerases involved in heptose modification have unique substrate / product specificities that can be exploited for biotechnological applications; (ii) novel putative methyl-transferases and a dedicated oxidase are involved in heptose modification and (iii) a novel regulator regulates heptose modification, capsule synthesis, and other surface carbohydrates.*** Our specific objectives are to:***1/ investigate the molecular basis for substrate / product specificities of heptose modifying epimerases and reductases.***2/ determine the role of putative methyltransferases, oxidase and regulator on heptose modification and production of capsule and other surface carbohydrates.*** The proposed research is of general significance as modified heptoses and other unusual sugars are found in surface carbohydrates of numerous bacteria. The information derived from our structure / function studies on determinants for substrate and product specificities will facilitate the elucidation of the synthesis pathways for other bacterial sugars. This research will also delineate regulatory mechanism involved in sugar synthesis to better understand the interplay between sugar synthesis pathways and their effect on bacterial physiology. Finally, this research will provide substrates enabling the studies of glycosyltransferases involved in the assembly of complex carbohydrate structures. This could lead to technological applications of heptose modifying enzymes for the production of complex carbohydrates.********