Crystal structure and refinement of cytochrome P450_terp at 2·3 Å resolution

Cytochrome P450_terp is a class I (mitochondrial/bacterial) P450 that catalyzes the hydroxylation of α-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 P6₁22, and cell dimensions a = b = 69·4 A ̊, c = 456·6 A ̊, α = β = 90°, γ = 120°. Diffraction data were collected at the Cornell High Energy Synchrotron Source, and the structure of P450_terp was solved by a combination of molecular replacement and multiple isomorphous replacement techniques. A model of P450_terp was built and refined against native data, to an R-factor of 18·9% for data with I ≥ σ(I) between 6·0 Å and 2·3 Å resolution. This model contains 412 of the 428 P450_terp amino acid residues; the loop between helices F and G is disordered in the crystal. While the overall fold of P450_terp is very similar to that of P450_cam, only three-quarters of the C^1α positions can be superimposed, to a root-mean-square deviation of only 1·87 Å. The mode of substrate binding by P450_terp 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.