Crystal structure and refinement of cytochrome P450terp at 2.3 A resolution.

C A Hasemann, K G Ravichandran, J A Peterson, J Deisenhofer

Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9050.

Journal of molecular biology 1994 Mar 4

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Cytochrome P450terp is a class I (mitochondrial/bacterial) P450 that catalyzes the hydroxylation of alpha-terpineol as part of the catabolic assimilation of this compound by a pseudomonad species. Crystals grown from the purified protein have the symmetry of space group P6(1)22, and cell dimensions a = b = 69.4 A, c = 456.6 A, alpha = beta = 90 degrees, gamma = 120 degrees. Diffraction data were collected at the Cornell High Energy Synchrotron Source, and the structure of P450terp was solved by a combination of molecular replacement and multiple isomorphous replacement techniques. A model of P450terp was built and refined against native data, to an R-factor of 18.9% for data with I > or = sigma(I) between 6.0 A and 2.3 A resolution. This model contains 412 of the 428 P450terp amino acid residues; the loop between helices F and G is disordered in the crystal. While the overall fold of P450terp is very similar to that of P450cam, only three-quarters of the C alpha positions can be superimposed, to a root-mean-square deviation of only 1.87 A. The mode of substrate binding by P450terp can be predicted, and probable substrate contact residues identified. The heme environment and side-chain positions in the adjacent I-helix suggest possible modes of proton delivery in the catalytic cycle of the enzyme.

Citation

C A Hasemann, K G Ravichandran, J A Peterson, J Deisenhofer. Crystal structure and refinement of cytochrome P450terp at 2.3 A resolution. Journal of molecular biology. 1994 Mar 4;236(4):1169-85