Structural Research of Transhydrogenases

Inquiry

Transhydrogenases (TH) are widely present in organisms and play essential roles in maintaining cellular redox homeostasis with implications for aging and many human diseases. Two types of TH have been found to exist in aerobic organisms, membrane-bound proton-pumping NADH: NADP⁺ oxidoreductase (PntAB) and membrane-independent soluble transhydrogenase (UdhA).

Advances in research on the structure of TH

TH exists as homodimers, each containing a proton translocation transmembrane structural domain and two soluble nucleotide-binding structural domains that mediate hydride transfer between NAD(H) and NADP(H). The three-domain structure of TH is conserved across species, but the polypeptide composition varies considerably. Researchers have analyzed the crystal structure of TH by single-particle cryo-electron microscopy, which helps to understand its role under pathological conditions, making it a potential target for new therapeutic strategies for oxidative stress-mediated diseases and cancer.

Molecular structure analysis of StnABC

StnABC acts as an electron-divergent transhydrogenase to catalyze reduction-dependent reactions. The researchers revealed the molecular structure of StnABC from S. ovata and observed that the complex consists of four protomers, each a StnABC heterotrimer. The tetrameric core consists of the StnC subunit of each protomer flanked by the more energetic StnAB subcomplexes, with only StnB binding to StnC, whereas StnA is found to interact with StnB through multiple contacts. The entire complex contains a large number of redox cofactors, and it is evident from the structure that the distances from all the iron-sulfur clusters to the sides of a single proto membrane ensure rapid electron transfer throughout the structure.

Figure 1. Molecular structure of StnABC. (Kumar A, et al., 2023)

Protein	Organism	Method	Resolution	PDB Entry ID
Transhydrogeanse domain II dimer	Thermus thermophilus HB27	X-ray diffraction	2.77 Å	4O93
Membrane-bound transhydrogenase	Thermus thermophilus	X-ray diffraction	2.2 Å	5UNI
Transhydrogenase in the apo state	Ovis aries	Cryo-EM single particle analysis	3.7 Å	6S59
Transhydrogenase domain I	Escherichia coli	X-ray diffraction	1.9 Å	1X13
Transhydrogenase domain I with bound NAD	Escherichia coli	X-ray diffraction	1.94 Å	1X14
Transhydrogenase domain I with bound NADH	Escherichia coli	X-ray diffraction	2.04 Å	1X15
Transhydrogenase dIII bound with NADPH	Homo sapiens	X-ray diffraction	2.2 Å	1U31
Transhydrogenase in the presence of NADP⁺ in a "single face-down" conformation	Ovis aries	Cryo-EM single particle analysis	3.7 Å	6QUE
Transhydrogenase in the presence of NADP⁺ in a "double face-down" conformation	Ovis aries	Cryo-EM single particle analysis	2.9 Å	6QTI
Transhydrogenase domain III	Bos taurus	X-ray diffraction	1.21 Å	1D4O
Transhydrogenase coupling proton translocation and hydride transfer	Thermus thermophilus HB27	X-ray diffraction	6.926 Å	4O9U
Transhydrogenase coupling proton translocation and hydride transfer	Thermus thermophilus HB27	X-ray diffraction	3.079 Å	4O9T
Transhydrogeanse domain II dimer SeMet derivative	Thermus thermophilus HB27	X-ray diffraction	1.89 Å	4OP9
The electron bifurcating transhydrogenase StnABC complex (state 1)	Sporomusa ovata DSM 2662	Cryo-EM single particle analysis	3.2 Å	8OH9
The electron bifurcating transhydrogenase StnABC complex (state 2)	Sporomusa ovata DSM 2662	Cryo-EM single particle analysis	3 Å	8OH5
Transhydrogenase domain III bound to NADPH	Rhodospirillum rubrum	X-ray diffraction	2.4 Å	1PNQ
Transhydrogenase domain I without bound NAD(H)	Rhodospirillum rubrum	X-ray diffraction	1.81 Å	1L7D
Transhydrogenase domain I with bound NADH	Rhodospirillum rubrum	X-ray diffraction	1.9 Å	1L7E
Transhydrogenase domain III bound to NADP	Rhodospirillum rubrum	X-ray diffraction	2.1 Å	1PNO
Transhydrogenase [(domain I)2: domain III] heterotrimer complex	Rhodospirillum rubrum	X-ray diffraction	3.1 Å	1XLT
Transhydrogenase (dI. Q132N)2(dIII)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	2.4 Å	1NM5
Transhydrogenase (dI. NADH)2(dIII.NADPH)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	3 Å	1U2D
Transhydrogenase (dI. R127A.NAD+)2(dIII.NADP⁺)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	2.6 Å	2FR8
Transhydrogenase (dI. S138A. NADH)2(dIII.NADPH)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	3.2 Å	2FRD
Transhydrogenase (dI.ADPr)2(dIII.NADPH)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	2.2 Å	1U2G
Transhydrogenase (dI.H2NADH)2(dIII.NADP⁺)1 asymmetric complex	Rhodospirillum rubrum	X-ray diffraction	2.6 Å	2OO5
DI and DIII complex of transhydrogenase with a thio-nicotinamide nucleotide analogue	Rhodospirillum rubrum	X-ray diffraction	2.61 Å	1PTJ

Table 1. Structural research of the transhydrogenases.

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References

Kumar A, et al. Molecular architecture and electron transfer pathway of the Stn family transhydrogenase. Nat Commun. 2023. 14(1): 5484.
Zhang Q, et al. Proton-translocating nicotinamide nucleotide transhydrogenase: a structural perspective. Front Physiol. 2017. 8: 1089.
Francisco A, et al. Mitochondrial NAD(P)+ Transhydrogenase: From Molecular Features to Physiology and Disease. Antioxid Redox Signal. 2022. 36(13-15): 864-884.