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 H(2)O and that H-bonds define its structure. A (15)N,(13)C 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 (15)N and C8 for residues R-I-R-III of the tetramer, indicating H-bonds between the (15)N's and the O8's of these residues. Additional J couplings between the (15)N's and C2's of the adjacent residues confirm the putative H-bonds. NH groups showing this long-range correlation also experience slower (1)H/(2)H 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 (2(4) helix) and 4 residues/turn (1(4) helix). To discriminate between models, we resorted to (1)H,(1)H NOEs. The 2(4) 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.
Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, Food and Drug Administration, 1401 Rockville Pike, Rockville, Maryland 20852-1448, USA.
Marcos D
MD
Battistel
Michael
M
Shangold
Loc
L
Trinh
Joseph
J
Shiloach
Darón I
DI
Freedberg
D000941:Antigens / Q000737:chemistry*; D002236:Carbohydrate Conformation; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry*
D000941:Antigens; D009844:Oligosaccharides; D019158:N-Acetylneuraminic Acid