CRYSTAL-STRUCTURE AND REFINEMENT OF CYTOCHROME P450(TERP) AT 2-CENTER-DOT-3 ANGSTROM RESOLUTION

Cytochrome P450terp 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 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 ≥ σ(I) between 6·0 Å and 2·3 Å 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 C1α positions can be superimposed, to a root-mean-square deviation of only 1·87 Å. 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. © 1994.