Solution structure of a trisaccharide-antibody complex : Comparison of NMR measurements with a crystal structure

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Journal titleBiochemistry
Pages51835192; # of pages: 10
Subjectpha; 13C; 13C-NMR; 1H; angle; antibodies; antibodies, monoclonal; antibody; antigen; antigen antibody complex; antigen-antibody complex; aqueous; aqueous-solution; binding; binding sites; binding sites, antibody; binding-site; bond; Canada; carbohydrate conformation; carbohydrate sequence; chemistry; comparative study; complex; complexes; conformation; conformational; conformations; constraints; crystal; crystal-structure; crystallography; crystallography, x-ray; distance; DMSO; energy; equilibrium; galactose; H-1; hydrogen; hydrogen bonding; immunology; ligand; lipopolysaccharide; lipopolysaccharides; magnetic resonance spectroscopy; methods; methyl; models, molecular; molecular; molecular sequence data; monoclonal-antibodies; monoclonal-antibody; NMR; NOE; oligosaccharide; protein; protein conformation; proton; protons; rates; residues; resolution; salmonella; site; sites; solid-state; solution; solution structure; solutions; state; structure; transferred; transferred NOE; trisaccharide; trisaccharides
AbstractNMR and crystallography have been used to study antigen conformational changes that occur in a trisaccharide-Fab complex in solution and in the solid state. NOE buildup rates from transferred NOE experiments show that the antigenic determinant of a Salmonella lipopolysaccharide, represented by the trisaccharide methly glycoside α-D-Galp(1→2)[α-D-Abep(1→3)]-α-D-Manp1→OMe (1), undergoes a protein-induced conformational shift about the Gal→Man glycosideic linkage when it is bound by a monoclonal antibody in awueous solution. the same trisaccharide was crystallized with Fab, and a solved structure at 2.1-Å resolution revealed that the conformation of the trisaccharide ligand was similar to that seen in a dodesaccharide-Fab complex [Cygler et al. (1991) Science 253, 442-445), where the Gal-Man linkage also experienced a similar conformational shift. Distance constraints derived from the TRNOE buildup curves are consistent with two bound trisaccharide conformations, one of which correlates with the ligand conformation of the crystalline Fab-trisaccaride complex. In this bound conformation, short interatomic distances between Abe O-2 and Gal O-2 permit an oligosaccharide intramolecular hydrogen bond. Despite its relatively low energy, a preponderance of this conformer could not be detected in awueous or DMSO solutions of free trisaccharide by either ¹H or ¹³CNMR experiments. In DMSO, a different intramolecular hydrogen bond between Abe O-2 and Man O-4 was observed due to a solvent-induced shift in the conformational equilibria (relative to aqueous solution). Molecular modeling of the trisaccharide in the binding site and as the free ligand suggested that the protein imposes an induced fit on the antigen, primarily resulting in a shift of the Gal-Man Ø torsional angle. This reduces the interproton separation between Abe H-3 and Gal H-1 with a marked increase in the intensity of the previously weak NOEs between the protons of the noncovalently linked galactose and abequose residues. The impact of the conformational shift on gross trisaccharide topology is sufficiently small that binding modes inferred from functional group replacements are not impaired.
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AffiliationNRC Biotechnology Research Institute; National Research Council Canada; NRC Institute for Biological Sciences
Peer reviewedNo
NRC number38487
NPARC number3539649
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Record identifierce18d9df-8c86-45f0-b470-4181dd21280c
Record created2009-03-01
Record modified2016-05-09
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