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Cytochromes P450 are important heme-containing enzymes that catalyze the oxidation of a vast array of endogenous and exogenous compounds, including drugs and carcinogens. One of the more successful approaches to study P450 function involves molecular modeling. Because none of the mammalian P450s have been crystallized, a number of homology models have been constructed based on the structures of known bacterial P450s. Molecular models, generated using molecular replacement or distance geometry methods, can be used to dock substrates and/or inhibitors in the active site to explain various aspects of enzyme function. The majority of modeling research has dealt with enzyme-substrate interactions in the active site. The analysis of these interactions has helped us to better understand the mechanism of P450 catalysis and provided the structural basis for the regio- and stereospecificity of substrate oxidation as well as susceptibility to inhibition or inactivation. The models have been utilized to identify and/or confirm key residues and to rationally interpret experimental data. The alteration in activity in a mutant P450 can be related to changes in enzyme-substrate/inhibitor interactions, such as the removal or appearance of van der Waals overlaps or changes in compound mobility. Homology models can also help to analyze P450-redox partner interactions and identify critical determinants of protein stability. We can expect further development of molecular modeling methods and their increasing contribution into research on P450 function as an integral part of a combined theoretical-experimental approach.

Cytochromes P450 form a very large superfamily of proteins which metabolize substrates from steroids to fatty acids to drugs and are found in organisms from protists to mammals. P450s all appear to take on a similar structural fold, yet frequently having less than 20% sequence identity and having vastly different substrates. Within the structural fold there appears to be a highly conserved core, as determined from the comparison of the structures of the six crystallized, soluble P450s. There are also variable regions which by and large appear to be associated with substrate recognition, substrate binding, and redox partner binding. Molecular dynamics simulations of motion in P450cam and P450BM-3 indicate that substrate binding and product release require substantial motion around the "substrate access channel." Additionally, at the 11th International Conference on Cytochrome P450 Biochemistry, Biophysics, and Molecular Biology and briefly here, the first structure of a microsomal eukaryotic P450 will be presented and compared to the already determined structures by Drs. Johnson and McRee. Finally, with a better understanding of the structure/function relationship of P450s, one will be better able to modify P450s to metabolize the substrates of choice or produce needed valuable chemicals., (Copyright 1999 Academic Press.)

Cytochromes P450 comprise a very large superfamily of hemeproteins which generally monooxygenate hydrophobic compounds. P450s appear to have a common conserved structural core, yet are variable in regions involved in substrate recognition and binding, and in redox-partner binding. These differences can be identified by an analysis in which structural alignments and homology models are used to compare the various classes and families of P450s.