RECEPTOR MAPPING WITH MULTIPLE BINDING MODES - BINDING-SITE OF A PCB-DEGRADING ENZYME

The binding site of a polychlorinated biphenyl (PCB)-degrading enzyme has been mapped using the published data on biodegradation rates of individual PCB congeners by the Acinetobacter P6 strain. As in other approaches to the problem, additivity of contributions of individual parts of the PCB molecules to the global binding energy was assumed. The compounds were allowed to bind to the enzyme in various binding modes. In the search for the correlation between the structure of individual PCB congeners and their biodegradation rates the approach to select one binding mode for each PCB congener failed. Its modification, the consideration of simultaneous occurrence of all possible binding modes for each PCB congener in proportions given by the binding energy provided satisfactory results. The resulting map of the binding site consists of four binding points corresponding to the positions (2 and 6), 5, 2', (3' and 4'), with both phenyl rings having a perpendicular orientation. The first binding point is attractive: the chlorines in the positions 2 and 6 are probably hydrophobically bonded to the counterparts in the binding site of the degrading enzyme. The other binding points are repulsive.