Abstract：
:Thebaine 6-O-demethylase (T6ODM) is an Fe(II)/2-oxoglutarate-dependent dioxygenase catalysing two oxidative O-demethylation reactions in morphine biosynthesis. Its crystal structure revealed a large active site pocket which is at least two times larger than necessary to accommodate a substrate (thebaine or oripavine) molecule. Since so far no crystal structures have been obtained for enzyme-substrate complex, which is necessary to explain the enzyme regiospecificity towards the C6-bound methoxy group, in this work we used computational methods and multi-parametric surface plasmon resonance measurements to elucidate the most likely structure of this complex and the reaction mechanism starting therefrom. Results of simulations and experiments unanimously indicate that the enzyme-substrate complex of T6ODM has a 1:2 stoichiometry. The key residues responsible for substrate binding are: Val-128, Glu-133, Met-150 and Agr-219 for the substrate in the distal position, and Asp-144, Leu-235 and Leu-353 for the proximal substrate molecule. QM/MM and DFT calculations show that the oxo ligand is bound trans to His-295 and the enzyme catalyzes hydroxylation of the C6-bound methoxy group according to the established rebound mechanism. The final stage of the demethylation reaction, which includes deformylation and enol-keton tautomerization steps, is most likely catalysed by water molecules and takes place in the solvent.
journal_name
Int J Biol Macromoljournal_title
International journal of biological macromoleculesauthors
Kachhap S,Wojdyla Z,Komorek P,Kluza A,Kurpiewska K,Jachimska B,Borowski Tdoi
10.1016/j.ijbiomac.2020.07.030subject
Has Abstractpub_date
2020-11-15 00:00:00pages
718-729eissn
0141-8130issn
1879-0003pii
S0141-8130(20)33755-7journal_volume
163pub_type
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