2 DISTINCT BINDING-SITES FOR GLOBOTRIAOSYL CERAMIDE ON VEROTOXINS - IDENTIFICATION BY MOLECULAR MODELING AND CONFIRMATION USING DEOXY ANALOGS AND A NEW GLYCOLIPID RECEPTOR FOR ALL VEROTOXINS

Background: The Escherichia coli verotoxins (VTs) can initiate human v ascular disease via the specific recognition of globotriaosyl-ceramide (Gb(3)) on target endothelial cells. To explore the structural basis for receptor recognition by different VTs we used molecular modelling based on the crystal structure of VT1, mutational data and binding dat a for deoxy galabiosyl receptors. Results: We propose a model for the verotoxin 'cleft-site complex' with Gb(3). Energy minimizations of Gb( 3) within the 'cleft site' of verotoxins VT1, VT2, VT2c and VT2e resul ted in stable complexes with hydrogen-bonding systems that were in agr eement with binding data obtained for mono-deoxy analogues of Gb(3). N -deacetylated globoside (aminoGb(4)), which was found to be a new, eff icient receptor for all verotoxins, can be favorably accommodated in t he cleft site of the VTs by formation of a salt bridge between the gal actosamine and a cluster of aspartates in the site. The model is furth er extended to explain the binding of globoside by VT2e. Docking data support the possibility of an additional binding site for Gb(3) on VT1 . Conclusions: The proposed models for the complexes of verotoxins wit h their globoglycolipid receptors are consistent with receptor analogu e binding data and explain previously published mutational studies. Th e results provide a first approach to the design of specific inhibitor s of VT-receptor binding.