Temperature dependencies of amide ¹H‐ and ¹⁵N‐chemical shifts in hyaluronan oligosaccharides

Abstract

Temperature coefficients (Deltadelta/DeltaT) of amide chemical shifts of N-acetylglucosamine residues have been measured in a range of oligosaccharides of the important vertebrate polysaccharide hyaluronan. Odd- and even-numbered oligosaccharides with glucuronic acid, Delta-4,5-unsaturated glucuronic acid and N-acetylglucosamine at the termini were investigated. All amide proton temperature coefficients were only slightly less negative (-6.9 to - 9.1 ppb/ degrees C) than those of amide protons in free exchange with water (approximately equal to -11 ppb/ degrees C), indicating an absence of persistent intramolecular hydrogen bonds. With the exception of amide groups in reducing-terminal N-acetylglucosamine rings, all amide proton environments have the same temperature coefficient (-6.9 ppb/ degrees C), irrespective of differences in amide group chemical shifts and (3)J(HH) coupling constants, i.e. they do not sense subtle differences in orientation of the amide group. Amide nitrogen temperature coefficients report the same phenomena but with greater sensitivity. These data provide a set of reference values for temperature coefficients measured in other carbohydrates with acetamido sugars.

Investigating the Molecular Basis for the Virulence of <i>Escherichia coli</i> K5 by Nuclear Magnetic Resonance Analysis of the Capsule Polysaccharide

“…The temperature coefficients of I ␣ and I ␤ rings are also large and, furthermore, indistinguishable from those of monosaccharide GlcNAc [Blundell and Almond, 2007]. These data indicate that the amide protons in K5 oligosaccharides are neither involved in intramolecular hydrogen bonds nor sterically occluded from water molecules [Cierpicki and Otlewski, 2001].…”

“…[ 1 H, 13 C]-HSQC spectra with and without 13 C-broadband decoupling disabled during acquisition were recorded at 13 C-natural abundance [Blundell et al, 2006b]. Amide temperature coefficients of chemical shifts ( ⌬ ␦ / ⌬ T) were derived from [ 1 H]-1D and [ 1 H, 15 N]-HSQC datasets recorded at 15 N-natural abundance and 750 MHz, as described previously [Blundell and Almond, 2007].…”

Less is more when simulating unsulfated glycosaminoglycan 3D‐structure: Comparison of GLYCAM06/TIP3P, PM3‐CARB1/TIP3P, and SCC‐DFTB‐D/TIP3P predictions with experiment

“…Our recent experimental observations 14 led to the hypothesis that two unsulfated chondroitin hexosamine hydroxyl hydrogen atoms (H-O4 and H-O6) are more solvent exposed in this carbohydrate backbone than in the hexosamine 4-epimerized hyaluronan backbone. Temperature coefficient experiments for chondroitin 14 and hyaluronan 66 have also shown the absence of persistent inter-residual hydrogen-bonding involving these atoms. The GLY-CAM06 RDF data illustrated in Figure 6 are consistent with these experimental observations and only GLYCAM06 (and to a lesser extent SCC-DFTB-D) could correctly predict hexosamine H-O4 to GlcA O5 hydrogen bond occupancies in Table 6.…”

Methods for Measuring Exchangeable Protons in Glycosaminoglycans

“…The sulfamate protons at the reducing (V) and nonreducing (I) ends have similar temperature coefficients, while the NH resonance labeled III is hardly affected by the increase in temperature, suggesting its involvement in a persistent hydrogen bond. Blundell N resonances of HA to demonstrate that the amide groups participate in transient rather than persistent hydrogen bonds as previously proposed [13,14]. In addition, Nestor et al used temperature coefficients as evidence for structural stabilization of HA through the participation of hydroxyl protons in hydrogen bonds [18].…”

“…As is the case for peptides and protons, the GAG amide protons exchange fairly slowly with water and can be detected over a wide range of pH values, with 90 % H 2 O/10 % D 2 O and pH 6.0 typical of conditions used for measurement of NMR spectra. Although lower temperatures are often used to slow the exchange rate and sharpen the resonances of exchangeable protons, amide protons, like those of HA, can be detected well above room temperature [13,14]. Recently, Langeslay and co-workers reported solution conditions that slow the rate of solvent exchange of the Hp and HS sulfamate protons and allow their detection by NMR [8].…”