Journal
GLYCOBIOLOGY
Volume 25, Issue 6, Pages 632-643Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/glycob/cwv006
Keywords
activated oligosaccharide; chitobiosyl; Class I hyaluronan synthase; polymer synthesis; reducing end elongation
Categories
Funding
- National Institute of General Medical Sciences from the National Institutes of Health [R01 GM35978]
Ask authors/readers for more resources
Class I hyaluronan synthases (HASs) assemble a polysaccharide containing the repeating disaccharide [GlcNAc(beta 1,4)GlcUA(beta 1,3)](n)-UDP and vertebrate HASs also assemble (GlcNAc-beta 1,4)(n) homo-oligomers (chitin) in the absence of GlcUA-UDP. This multi-membrane domain CAZy GT2 family glycosyltransferase, which couples HA synthesis and translocation across the cell membrane, is atypical in that monosaccharides are incrementally assembled at the reducing, rather than the non-reducing, end of the growing polymer. Using Escherichia coli membranes containing recombinant Streptococcus equisimilis HAS, we demonstrate that a prokaryotic Class I HAS also synthesizes chitin oligomers (up to 15-mers, based on MS and MS/MS analyses of permethylated products). Furthermore, chitin oligomers were found attached at their reducing end to -4GlcNAc(alpha 1 ->)UDP [i.e. (GlcNAc beta 1,4)(n)GlcNAc(alpha 1 ->)UDP]. These oligomers, which contained up to at least seven HexNAc residues, consisted of beta 4-linked GlcNAc residues, based on the sensitivity of the native products to jack bean beta-N-acetylhexosaminidase. Interestingly, these oligomers exhibited mass defects of -2, or -4 for longer oligomers, that strictly depended on conjugation to UDP, but MS/MS analyses indicate that these species result from chemical dehydrogenations occurring in the gas phase. Identification of (GlcNAc-beta 1,4)(n)-GlcNAc(alpha 1 ->)UDP as HAS reaction products, made in the presence of GlcNAc(alpha 1 ->)UDP only, provides strong independent confirmation for the reducing terminal addition mechanism. We conclude that chitin oligomer products made by HAS are derived from the cleavage of these novel activated oligo-chitosyl-UDP oligomers. Furthermore, it is possible that these UDP-activated chitin oligomers could serve as self-assembled primers for initiating HA synthesis and ultimately modify the non-reducing terminus of HA with a chitin cap.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available