title: Conformational analysis of the sialyl alpha(2----3/6)N-acetyllactosamine structural element occurring in glycoproteins, by two-dimensional NOE 1H-NMR spectroscopy in combination with energy calculations by hard-sphere exo-anomeric and molecular mechanics force-field with hydrogen-bonding potential.
abstract: The conformation is described of the sialyl alpha(2----3/6)N-acetyllactosamine structural element, frequently occurring in glycoproteins. NOE spectroscopy of NeuAc alpha(2----3)Gal beta(1----4)GlcNAc beta(1----N)Asn and NeuAc alpha(2----6)Gal beta(1----4)GlcNAc beta(1----N)Asn is presented and for each glycosidic linkage, except for the alpha(2----6)-linkage, a number of interglycosidic NOEs are measured. The analysis of these effects is performed using a full relaxation matrix. Analysis of intraresidue NOEs provides a calibration of the calculation method. Hard-sphere exo-anomeric (HSEA) energy calculations indicate a single conformation for the beta(1----4)-linkage in both compounds, both being consistent with the NOE data. HSEA and molecular-mechanics force-field with hydrogen-bonding potential energy calculations both indicate the existence of three preferred conformations for the alpha(2----3)-linkage. The analysis of the NOE spectra are consistent with a distribution over two or three of these conformations; by combination with the energy diagram for this linkage the existence of onyl a single conformation can be excluded. The NOE spectrum of the compound with the alpha(2----6)-linkage indicates a gt orientation for the Gal C-6 hydroxymethyl group. On this basis, the HSEA energy calculations for the alpha(2----6)-linkage indicate an extended low-energy surface with a number of preferred conformations. The absence of NOEs across this linkage is interpreted in terms of a non-rigid, but overall folded conformation of the NeuAc alpha(2----6)Gal beta(1----4)GlcNAc beta structural element. This provides an explanation for the shift effects induced by alpha(2----6) attachment of NeuAc to the N-acetyllactosamine unit.
authors.affiliation: Department of Bio-Organic Chemistry, University of Utrecht, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Breg
authors.forename: L M
authors.initials: LM
authors.lastname: Kroon-Batenburg
authors.forename: G
authors.initials: G
authors.lastname: Strecker
authors.forename: J
authors.initials: J
authors.lastname: Montreuil
authors.forename: J F
authors.initials: JF
authors.lastname: Vliegenthart
mesh_terms: D000606:Amino Sugars; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D006023:Glycoproteins; D006801:Humans; D006859:Hydrogen; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000302:isolation & purification / Q000652:urine
chemical_list: D000606:Amino Sugars; D006023:Glycoproteins; D009844:Oligosaccharides; C032269:sialyl-N-acetyllactosamine; D006859:Hydrogen