CONSTRUCTION OF A 3D MODEL OF CYTOCHROME-P450 2B4

A three-dimensional structural model of rabbit phenobarbital-inducible cytochrome P450 2B4 (LM2) was constructed by homology modeling techni ques previously developed for building and evaluating a 3D model of th e cytochrome P450choP isozyme. Four templates with known crystal struc tures including cytochrome P450cam, terp, BM-3 and eryF were used in m ultiple sequence alignments and construction of the cytochrome P450 2B 4 coordinates, The model was evaluated for its overall quality using a vailable protein analysis programs and found to be satisfactory. The m odel structure was stable at room temperature during a 140 ps unconstr ained full protein molecular dynamics simulation. A putative substrate access channel and binding site were identified. Two different substr ates, benzphetamine and androstenedione, that are metabolized by cytoc hrome P450 2B4 with pronounced product specificity were docked into th e putative binding site. Two orientations were found for each substrat e that could lead to the observed preferred products. Using a geometri c fit method three regions on the surface of the model cytochrome P450 structure were identified as possible sites for interaction with cyto chrome b(5), a redox partner of P450 2B4. Residues that may interact w ith the substrates and with cytochrome b(5) have been identified and m utagenesis studies are currently in progress.