5t6q
Structure of cytochrome P450 4B1 (CYP4B1) complexed with octane: An n-Alkane and fatty acid omega-hydroxylase with a covalently bound heme
Structural highlights
FunctionCP4B1_RABIT Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It oxidizes a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. Publication Abstract from PubMedP450 family 4 fatty acid omega-hydroxylases preferentially oxygenate primary C-H bonds over adjacent, energetically favored secondary C-H bonds, but the mechanism explaining this intriguing preference is unclear. To this end, the structure of rabbit P450 4B1 complexed with its substrate octane was determined by X-ray crystallography to define features of the active site that contribute to a preference for omega-hydroxylation. The structure indicated that octane is bound in a narrow active site cavity that limits access of the secondary C-H bond to the reactive intermediate. A highly conserved sequence motif on helix I contributes to positioning the terminal carbon of octane for omega-hydroxylation. Glu-310 of this motif auto-catalytically forms an ester bond with the heme 5-methyl, and the immobilized E310 contributes to substrate positioning. The preference for omega-hydroxylation was decreased in a E310A mutant having a shorter side-chain, but overall rates of metabolism were retained. E310D and E310Q substitutions having longer side-chains exhibit lower overall rates, likely due to higher conformational entropy for these residues, but they retained high preferences for octane omega-hydroxylation. Sequence comparisons indicated that active-site residues constraining octane for omega-hydroxylation are conserved in family 4 P450s. Moreover, the heme 7-propionate is positioned in the active site and provides additional restraints on substrate binding. In conclusion, P450 4B1 exhibits structural adaptations for omega-hydroxylation that include changes in the conformation of the heme and changes in a highly conserved helix I motif that is associated with selective oxygenation of un-activated primary C-H bonds. The Crystal Structure of Cytochrome P450 4B1 (CYP4B1) Monoxygenase Complexed with Octane Discloses Several Structural Adaptations for omega-Hydroxylation.,Hsu MH, Baer BR, Rettie AE, Johnson EF J Biol Chem. 2017 Feb 6. pii: jbc.M117.775494. doi: 10.1074/jbc.M117.775494. PMID:28167536[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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