Evidence for Helical Structure in a Tetramer of α2-8 Sialic Acid: Unveiling a Structural Antigen

Characteristic H-bonding patterns define secondary structure in proteins and nucleic acids. We show that similar patterns apply for α2-8 sialic acid (SiA) in H2O and that H-bonds define its structure. A 15N,13C α2-8 SiA tetramer, (SiA)4, was used as a model system for the polymer. At 263 K, we detec...

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Bibliographic Details
Published in:	Journal of the American Chemical Society Vol. 134; no. 26; pp. 10717 - 10720
Main Authors:	Battistel, Marcos D., Shangold, Michael, Trinh, Loc, Shiloach, Joseph, Freedberg, Darón I.
Format:	Journal Article
Language:	English
Published:	United States American Chemical Society 04-07-2012
Subjects:	Antigens - chemistry Carbohydrate Conformation Hydrogen Bonding Magnetic Resonance Spectroscopy N-Acetylneuraminic Acid - chemistry Oligosaccharides - chemistry
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Summary:	Characteristic H-bonding patterns define secondary structure in proteins and nucleic acids. We show that similar patterns apply for α2-8 sialic acid (SiA) in H2O and that H-bonds define its structure. A 15N,13C α2-8 SiA tetramer, (SiA)4, was used as a model system for the polymer. At 263 K, we detected intra-residue through-H-bond J couplings between 15N and C8 for residues R-I–R‑III of the tetramer, indicating H-bonds between the 15N’s and the O8’s of these residues. Additional J couplings between the 15N’s and C2’s of the adjacent residues confirm the putative H-bonds. NH groups showing this long-range correlation also experience slower 1H/2H exchange. Additionally, detection of couplings between H7 and C2 for R-II and R-III implies that the conformations of the linkers between these residues are different than in the monomers. These structural elements are consistent with two left-handed helical models: 2 residues/turn (24 helix) and 4 residues/turn (14 helix). To discriminate between models, we resorted to 1H,1H NOEs. The 24 helical model is in better agreement with the experimental data. We provide direct evidence of H-bonding for (SiA)4 and show how H-bonds can be a determining factor for shaping its 3D structure.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0002-7863 1520-5126
DOI:	10.1021/ja300624j