X-ray crystal structure and catalytic properties of Thr252Ile mutant of cytochrome P450cam: roles of Thr252 and water in the active center.
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Hishiki T, Shimada H, Nagano S, Egawa T, Kanamori Y, Makino R, Park SY, Adachi S, Shiro Y, Ishimura Y
X-ray crystal structure and catalytic properties of Thr252Ile mutant of cytochrome P450cam: roles of Thr252 and water in the active center.
J Biochem. 2000 Dec;128(6):965-74.
- PubMed ID
- 11098139 [ View in PubMed]
- Abstract
The structure-function relationship in cytochrome P450cam monooxygenase was studied by employing its active site mutant Thr252Ile. X-ray crystallographic analyses of the ferric d-camphor-bound form of the mutant revealed that the mutation caused a structural change in the active site giving an enlarged oxygen-binding pocket that did not contain any hydrophilic group such as the OH group of Thr and H(2)O. The enzyme showed a low monooxygenase activity of ca. 1/10 of the activity of the wild-type enzyme. Kinetic analyses of each catalytic step revealed that the rate of proton-coupled reduction of the oxygenated intermediate of the enzyme, a ternary complex of dioxygen and d-camphor with the ferrous enzyme, decreased to about 1/30 of that of the wild-type enzyme, while the rates of other catalytic steps including the reduction of the ferric d-camphor-bound form by reduced putidaredoxin did not change significantly. These results indicated that a hydrophilic group(s) such as water and/or hydroxyl group in the active site is prerequisite to a proton supply for the reduction of the oxygenated intermediate, thereby giving support for the operation of a proton transfer network composed of Thr252, Asp251, and two other amino acids and water proposed by previous investigators.