Structural stability and dynamics of hydrogenated and perdeuterated cytochrome P450cam (CYP101)

Perdeuterated and hydrogenated cytochrome P450cam (P450cam), from Pseudomonas putida, has been characterized concerning thermal stability and structural dynamics. For the first time, Fourier transform infrared (FTIR) spectroscopy was used to characterize a perdeuterated protein. The secondary structure compositions were determined from the fitted amide I′ spectral region, giving band populations at 10 °C for the perdeuterated protein of 22% between 1605 and 1624 cm^-1 (β-sheets), 47% between 1633 and 1650 cm^-1 (α-helix (29%) plus unordered/3₁₀-helix (18%)), and 28% between 1657 and 1677 cm^-1 (turns) and for the hydrogenated protein of 22% between 1610 and 1635 cm^-1 (β-sheets), 52% between 1640 and 1658 cm^-1 (α-helix (41%) plus unordered/3₁₀-helix (11%)), and 24% between 1665 and 1680 cm^-1 (turns). Thermal unfolding experiments revealed that perdeuterated P450cam was less stable than the hydrogenated protein. The midpoint transition temperatures were 60.8 and 64.4 °C for the perdeuterated and hydrogenated P450cam, respectively. Step-scan time-resolved FTIR was applied to the P450cam-CO complex to study the ligand-rebinding process after flash photolysis. Rebinding of the ligand occurred with the same kinetics and rate constants k_on, 8.9 × 10⁴ and 8.3 × 10⁴ M^-1 s^-1 for the perdeuterated and hydrogenated P450cam, respectively. Perdeuterated P450cam was expressed for a neutron crystallographic study to determine the specific hydration states and hydrogen-bonding networks at the active site. The analyses presented here show that perdeuterated P450cam is structurally similar to its hydrogenated counterpart, despite its reduced thermal stability, suggesting that information obtained from the neutron structure will be representative of the normal hydrogenated P450cam.