Structural Research of Membrane-bound Oxidoreductases

In biochemistry, oxidoreductase enzymes catalyze the transfer of electrons from one molecule (the reductant, also known as the electron donor) to another (the oxidant, also known as the electron acceptor). The process typically utilizes NADP⁺ or NAD⁺ as a cofactor. Understanding the structure and function of oxidoreductases is critical to improving our ability to manipulate the oxidoreductase catalytic pathway for various applications. In recent years, significant progress has been made in structural studies of oxidoreductases, providing new insights into their catalytic mechanisms.

Structural research on membrane-bound dihydroorotate, quinone oxidoreductase (DHOQO)

Dihydroorotate, quinone oxidoreductase (DHOQO) is a flavin mononucleotide (FMN)-containing membrane-bound enzyme responsible for oxidizing dihydroorotate (DHO) to orotate with concomitant reduction of quinone to quinol. DHOQOs belong to the octet βα barrel family (βα)8, with a central core of eight parallel β chains (β1-β8) surrounded by eight α-helices (α1-α8). One side of the core has three β chains (βc-βe), often called the top side, and the other side has two (βa-βb), called the bottom side, totaling 13 β chains.

Structural studies of NADPH-cytochrome P450 oxidoreductase (CYPOR)

CYPOR is an essential flavoprotein of the microsomal cytochrome P450-monooxygenase system that transfers electrons from NADPH to FAD to FMN to members of the cytochrome P450 superfamily. It is anchored in the phospholipid bilayer by its amino-terminal membrane-bound structural domain. The structure of rat CYPOR at 2.6Å resolution confirms the presence of four separate domains, including FMN, the linker domain, FAD, and the NADPH-binding domain. The linker domain brings the two flavin structural domains close to facilitate internal electron transfer within CYPOR to interact with P450.

Figure 1. Orientation of CYPOR on membranes. (Xia C, et al., 2019)

Protein	Organism	Method	Resolution	PDB Entry ID
L-amino acid deaminase	Proteus vulgaris	X-ray diffraction	2.63 Å	5HXW
A respiratory membrane-bound hydrogenase	Pyrococcus furiosus COM1 Pyrococcus furiosus DSM 3638	Cryo-EM single particle analysis	3.7 Å	6CFW
Particulate methane monooxygenase	Methylocystis sp. ATCC 49242	X-ray diffraction	3.15 Å	4PI0
Particulate methane monooxygenase	Methylocystis sp. ATCC 49242	X-ray diffraction	3.59 Å	4PHZ
Particulate methane monooxygenase	Methylococcus capsulatus Methylococcus capsulatus str. Bath	X-ray diffraction	2.801 Å	1YEW
Cytochrome c nitrite reductase NrfHA complex	Desulfovibrio vulgaris str. Hildenborough	X-ray diffraction	2.3 Å	2J7A
Membrane-bound respiratory [NiFe] hydrogenase in an H2-reduced condition	Hydrogenovibrio marinus	X-ray diffraction	1.18 Å	3AYX
Membrane-bound respiratory [NiFe] hydrogenase in an air-oxidized condition	Hydrogenovibrio marinus	X-ray diffraction	1.22 Å	3AYZ
Membrane-bound respiratory [NiFe]-hydrogenase in a ferricyanide-oxidized condition	Hydrogenovibrio marinus	X-ray diffraction	1.32 Å	5Y34
Membrane-bound alcohol dehydrogenase	Gluconobacter oxydans Gluconobacter oxydans 621H	Cryo-EM single particle analysis	2.5 Å	8GY2
Krypton derivatization of an O2-tolerant membrane-bound [NiFe] hydrogenase	Cupriavidus necator	X-ray diffraction	1.47 Å	5D51
Membrane-bound manganese superoxide dismutase	Nostoc sp. PCC 7120 = FACHB-418	X-ray diffraction	2 Å	1GV3
Hydrogenase-1 in complex with cytochrome b	Escherichia coli K-12	X-ray diffraction	3.3 Å	4GD3
Gamma-alpha subunit complex from glucose dehydrogenase	Burkholderia cepacia	X-ray diffraction	2.6 Å	6A2U
H2-reduced structure of hydrogenase-1	Escherichia coli	X-ray diffraction	1.47 Å	3UQY
A novel membrane-bound 6-phosphogluconate dehydrogenase	Gluconacetobacter diazotrophicus PA1 5	X-ray diffraction	1.87 Å	6VPB
Membrane-bound aldehyde dehydrogenase	Gluconobacter oxydans	Cryo-EM single particle analysis	2.7 Å	8GY3
O2-tolerant MBH-P242C in its reduced state	Cupriavidus necator H16	X-ray diffraction	1.62 Å	7ODG
Cytochrome bd-II type oxidase with bound aurachin D	Escherichia coli BW25113	Cryo-EM single particle analysis	3 Å	7OSE
MdbA protein, a thiol-disulfide oxidoreductase	Corynebacterium diphtheriae NCTC 13129	X-ray diffraction	1.77 Å	5C00
The lipoyl domain of the chimeric dihydrolipoyl dehydrogenase P64K	Neisseria meningitidis	SOLUTION NMR	/	1GJX
R. rubrum transhydrogenase domain III bound to NADPH	Rhodospirillum rubrum	X-ray diffraction	2.4 Å	1PNQ
Oxidized active mutant of (S)-mandelate dehydrogenase	Pseudomonas putida Spinacia oleracea	Cryo-EM single particle analysis	1.35 Å	1P4C

Table 1. Structural research of oxidoreductases.

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References

Xia C, et al. Structural and Functional Studies of the Membrane-Binding Domain of NADPH-Cytochrome P450 Oxidoreductase. Biochemistry. 2019. 58(19):2408-2418.
Sousa FM, et al. Investigating the amino acid sequences of membrane bound dihydroorotate: quinone oxidoreductases (DHOQOs): Structural and functional implications. Biochim Biophys Acta Bioenerg. 2021.1862(1):148321.
Jensen K, Møller BL. Plant NADPH-cytochrome P450 oxidoreductases. Phytochemistry. 2010. 71(2-3):132-141.