Second-generation mimics of ganglioside GM1 oligosaccharide: a three-dimensional view of their interactions with bacterial enterotoxins by NMR and computational methods.
As a step to delineate a strategy of ligand design for cholera toxin (CT), NMR studies were performed on several mimics of the GM1 ganglioside oligosaccharide. The conformation of these analogues was investigated first in solution and then upon binding to cholera toxin by transferred nuclear Overhauser effect (TR-NOE) measurements. It was demonstrated that CT selects a conformation similar to the global minima of the free saccharides from the ensemble of presented conformations. No evidence of major conformational distortions was obtained, but one or two of the available conformers of the hydroxyacid side chain appear to be selected in the bound state. The NMR data were interpreted with the aid of computer models, generated and analyzed by using a combination of different approaches (MacroModels' MC/EM and MC/SD, Autodock, and GRID). Analysis of the NMR data supported by computational studies allowed us to interpret the experimental observations and to derive workable models of the ligand:toxin complexes. These models suggest that the higher affinity of the (R)-lactic acid derivative 3 may stem from lipophilic interactions with a hydrophobic area in the toxin binding site located in the vicinity of the sialic acid side chain binding region of the CT:GM1 complex, and formed by the side chain of Ile-58 and Lys-34. Thus, the models obtained have allowed us to make useful design suggestions for the improvement of ligand affinity.
Bernardi
Anna
A
Dipartimento di Chimica Organica e Industriale Universita' di Milano, and Centro di Eccellenza CISI via Venezian 21, 20133 Milano, Italy. anna.bernardi@unimi.it
Potenza
Donatella
D
Capelli
Anna Maria
AM
García-Herrero
Alicia
A
Cañada
F Javier
FJ
Jiménez-Barbero
Jesús
J
D001665:Binding Sites; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000737:chemistry; D003198:Computer Simulation; D004768:Enterotoxins / Q000737:chemistry* / Q000378:metabolism; D005677:G(M1) Ganglioside / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D018716:Molecular Mimicry; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D011506:Proteins / Q000737:chemistry
D002241:Carbohydrates; D004768:Enterotoxins; D008024:Ligands; D009844:Oligosaccharides; D011506:Proteins; D005677:G(M1) Ganglioside