MODELING OF THE INTERACTION OF VEROTOXIN-1 (VT1) WITH ITS GLYCOLIPID RECEPTOR, GLOBOTRIAOSYLCERAMIDE (GB(3))

Possible binding sites for the glycolipid globotriaosylceramide (Gal a lpha 1 --> 4Gal beta 1 --> 4Glc beta 1 --> 1Cer; Gb(3)) on the B-subun its of verotoxin-1 (VT1) were explored using binding data for specific ally mutated verotoxins and by computational docking of favoured confo rmers of Gb(3) with the crystal structure of VT1. Calculations using t he GRID program suggested a site with favourable hydrophobic interacti ons at the exposed side chain of Phe30. One of the favoured conformers of Gb(3) was docked into this site, with the hydrophobic face of the internal Gal beta residue in contact with the side chain of Phe30. Aft er energy minimization, the two terminal saccharide residues of Gb(3) (Gal alpha and Gal beta) showed favourable interactions with the toxin . in the proposed model of the complex, the terminal Gal alpha of Gb(3 ) is located in proximity to aspartates 16-18 of VT1. The model is in agreement with available experimental binding data for the interaction of globoglycolipids with different naturally occurring and mutated ve rotoxins.