MOLECULAR MODELING OF THE INTERACTION BETWEEN DCMU AND THE Q(B)-BINDING SITE OF PHOTOSYSTEM-II

The prefered binding orientations for the herbicide DCMU within the Q( B)-binding site of the D1 protein model from a photosystem II reaction centre have been determined. Calculation of the intermolecular energy between the herbicide and the binding site has been instrumental in o btaining optimum positions reinforced by experimental results from mut ation studies and herbicide binding to analogous bacterial reaction ce ntres. We have shown that two binding sites are possible, one involvin g a hydrogen bond to the His 215 residue of the Q(B)-binding site and the other to the Ser 264 residue. In both cases, it appears to be the van der Waals forces which are more important for the stabilization of the interactions.