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Int J Mol Sci ; 23(5)2022 Feb 23.
Article in English | MEDLINE | ID: covidwho-1736941


The fourth enzymatic reaction in the de novo pyrimidine biosynthesis, the oxidation of dihydroorotate to orotate, is catalyzed by dihydroorotate dehydrogenase (DHODH). Enzymes belonging to the DHODH Class II are membrane-bound proteins that use ubiquinones as their electron acceptors. We have designed this study to understand the interaction of an N-terminally truncated human DHODH (HsΔ29DHODH) and the DHODH from Escherichia coli (EcDHODH) with ubiquinone (Q10) in supported lipid membranes using neutron reflectometry (NR). NR has allowed us to determine in situ, under solution conditions, how the enzymes bind to lipid membranes and to unambiguously resolve the location of Q10. Q10 is exclusively located at the center of all of the lipid bilayers investigated, and upon binding, both of the DHODHs penetrate into the hydrophobic region of the outer lipid leaflet towards the Q10. We therefore show that the interaction between the soluble enzymes and the membrane-embedded Q10 is mediated by enzyme penetration. We can also show that EcDHODH binds more efficiently to the surface of simple bilayers consisting of 1-palmitoyl, 2-oleoyl phosphatidylcholine, and tetraoleoyl cardiolipin than HsΔ29DHODH, but does not penetrate into the lipids to the same degree. Our results also highlight the importance of Q10, as well as lipid composition, on enzyme binding.

Dihydroorotate Dehydrogenase/chemistry , Dihydroorotate Dehydrogenase/metabolism , Escherichia coli/enzymology , Lipid Bilayers/metabolism , Ubiquinone/metabolism , Cardiolipins/metabolism , Escherichia coli Proteins/chemistry , Escherichia coli Proteins/metabolism , Humans , Hydrophobic and Hydrophilic Interactions , Models, Molecular , Phosphatidylcholines/metabolism , Protein Conformation , Protein Domains