Cytochromes<i>b</i>561: Ascorbate-Mediated Trans-Membrane Electron Transport

Asard, Han; Barbaro, Raffaella; Trost, Paolo; Bérczi, Alajos

doi:10.1089/ars.2012.5065

Cited by 88 publications

(90 citation statements)

References 60 publications

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“…Monodehydroascorbate likely binds to His 106 of A. thaliana Cytb 561 -B or the corresponding residues in other homologs, accepting an electron, incorporating a proton, and producing one molecule of ascorbate. This model is consistent with the observations that the concentration of ascorbate is higher in the cytoplasm than on the other side (32), whereas the concentration of proton is the opposite (35). During the electron transfer process, Lys 81 on the cytoplasmic side and His 106 on the noncytoplasmic side might be involved not only in substrate recognition but in catalysis, perhaps through cycles of protonation and deprotonation.…”

Section: Discussionsupporting

confidence: 90%

See 1 more Smart Citation

Structure and mechanism of a eukaryotic transmembrane ascorbate-dependent oxidoreductase

Lu¹,

Ma²,

Yan

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

102

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Vitamin C, also known as ascorbate, is required in numerous essential metabolic reactions in eukaryotes. The eukaryotic ascorbate-dependent oxidoreductase cytochrome b 561 (Cyt b 561 ), a family of highly conserved transmembrane enzymes, plays an important role in ascorbate recycling and iron absorption. Although Cyt b 561 was identified four decades ago, its atomic structure and functional mechanism remain largely unknown. Here, we report the high-resolution crystal structures of cytochrome b 561 from Arabidopsis thaliana in both substrate-free and substratebound states. Cyt b 561 forms a homodimer, with each protomer consisting of six transmembrane helices and two heme groups. The negatively charged substrate ascorbate, or monodehydroascorbate, is enclosed in a positively charged pocket on either side of the membrane. Two highly conserved amino acids, Lys 81 and His 106, play an essential role in substrate recognition and catalysis. Our structural and biochemical analyses allow the proposition of a general electron transfer mechanism for members of the Cyt b 561 family. V itamin C, an essential nutrient for humans (1), is important for the synthesis of collagen (2), carnitine (3), and the neurotransmitter norepinephrine (4). Vitamin C also plays an important role in protection against oxidative stress (5). Oxidation of ascorbate results in sequential production of monodehydroascorbate and dehydroascorbate through loss of one and two electrons, respectively (6). Ascorbate serves as an electron donor for various enzymes, such as prolyl and lysyl hydroxylase, dopamine β-hydroxylase, ascorbate peroxidase, and cytochrome b 561 (Cyt b 561 ). Cyt b 561 , initially identified in the chromaffin granules of bovine adrenal medullae about 40 y ago (7,8), is a transmembrane ascorbate-dependent oxidoreductase (9-13) that plays a key role in ascorbate recycling and other physiological processes, such as iron absorption (14). To our knowledge, Cyt b 561 is the only membrane-embedded oxidoreductase that relies on ascorbate as the electron donor.Homologs resides in the chromaffin vesicle membrane and transfers electrons from cytoplasmic ascorbate to the intravesicular monodehydroascorbate radical for the regeneration of ascorbate (9, 13, 16), which is a substrate of dopamine β-hydroxylase for the synthesis of neurotransmitter norepinephrine. DCyt b 561 is present in the duodenal mucosa cell membrane, where it relays electrons from cytoplasmic ascorbate to ferric-chelate in the intestinal lumen, yielding soluble ferrous ion for absorption via a Fe 2+ -transporter (17-20). Expression levels of DCyt b 561 in the duodenal mucosa cell membrane are closely associated with iron metabolism disorders, such as chronic anemia and iron-deficiency anemia (19). Similar to CGCyt b 561 , ZmCyt b 561 uses ascorbate and the monodehydroascorbate radical as the physiological electron donor and acceptor, respectively (11,21,22).Despite rigorous investigation, there is no detailed structural information for any member of the Cyt b 561 family. Cons...

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Section: Discussionsupporting

confidence: 90%

“…3B) , all residues that interact with monodehydroascorbate are highly conserved among members of the Cyt b 561 family. Notably, these substrate-binding residues observed in our crystal structures are different from the predicted substrate-binding motifs ALLVYR (residues 66-71) and SLHSW (residues 116-120) (14,19,32) (Fig. S3).…”

Section: Resultsmentioning

confidence: 56%

Structure and mechanism of a eukaryotic transmembrane ascorbate-dependent oxidoreductase

Lu¹,

Ma²,

Yan

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

102

View full text Add to dashboard Cite

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“…Cytochrome b561, localized in cell walls, has also been shown to have MDHAR activity and can reduce the MDHA radical. This reduction leads to transport of electrons across the cell wall and thus to redox modifications which should allow cell wall expansion (Asard et al 2013;Horemans et al 2000Horemans et al , 1994. The AsA/DHA couple redox status is not involved (Kato & Esaka 1999).…”

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confidence: 99%

Reduction of MDHAR activity in cherry tomato suppresses growth and yield and MDHAR activity is correlated with sugar levels under high light

Truffault

Gest

Garchery

et al. 2016

Plant Cell & Environment

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Ascorbate is oxidized into the radical monodehydroascorbate (MDHA) through ascorbate oxidase or peroxidase activity or non-enzymatically by reactive oxygen species. Regeneration of ascorbate from MDHA is ensured by the enzyme MDHA reductase (MDHAR). Previous work has shown that growth processes and yield can be altered by modifying the activity of enzymes that recycle ascorbate; therefore, we have studied similar processes in cherry tomato (Solanum lycopersium L.) under- or overexpressing MDHAR. Physiological and metabolic characterization of these lines was carried out under different light conditions or by manipulating the source-sink ratio. Independently of the light regime, slower early growth of all organs was observed in MDHAR silenced lines, decreasing final fruit yield. Photosynthesis was altered as was the accumulation of hexoses and sucrose in a light-dependent manner in plantlets. Sucrose accumulation was also repressed in young fruits and final yield of MDHAR silenced lines showed a stronger decrease under carbon limitation, and the phenotype was partially restored by reducing fruit load. Ascorbate and MDHA appear to be involved in control of growth and sugar metabolism in cherry tomato and the associated enzymes could be potential targets for yield improvement.

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“…This type of electron transport was mediated by a single transmembrane cytochrome; it was stimulated by cytosolic ascorbate and required an artificial electron acceptor like ferricyanide on the external face of the membrane. CYBDOM proteins contain three hemes, two in the transmembrane cytochrome b561 domain and a third one in the extracellular DOMON domain (Asard et al 2013). AIR12 contains a single DOMON domain attached to the external face of the plasma membrane by a phosphatidylinositol anchor (Preger et al 2009).…”

Section: Discussionmentioning

confidence: 99%

Role of the NAD(P)H quinone oxidoreductase NQR and the cytochrome b AIR12 in controlling superoxide generation at the plasma membrane

Biniek

Heyno

Kruk

et al. 2016

Planta

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The quinone reductase NQR and the b-type cytochrome AIR12 of the plasma membrane are important for the control of reactive oxygen species in the apoplast. AIR12 and NQR are two proteins attached to the plant plasma membrane which may be important for generating and controlling levels of reactive oxygen species in the apoplast. AIR12 (Auxin Induced in Root culture) is a single gene of Arabidopsis that codes for a mono-heme cytochrome b. The NADPH quinone oxidoreductase NQR is a two-electron-transferring flavoenzyme that contributes to the generation of O in isolated plasma membranes. A. thaliana double knockout plants of both NQR and AIR12 generated more O and germinated faster than the single mutant affected in AIR12. To test whether NQR and AIR12 are able to interact functionally, recombinant purified proteins were added to plasma membranes isolated from soybean hypocotyls. In vitro NADH-dependent O production at the plasma membrane in the presence of NQR was reduced upon addition of AIR12. Electron donation from semi-reduced menadione to AIR12 was shown to take place. Biochemical analysis showed that purified plasma membrane from soybean hypocotyls or roots contained phylloquinone and menaquinone-4 as redox carriers. This is the first report on the occurrence of menaquinone-4 in eukaryotic photosynthetic organisms. We propose that NQR and AIR12 interact via the quinone, allowing an electron transfer from cytosolic NAD(P)H to apoplastic monodehydroascorbate and control thereby the level of reactive oxygen production and the redox state of the apoplast.

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Cytochromesb561: Ascorbate-Mediated Trans-Membrane Electron Transport

Cited by 88 publications

References 60 publications

Structure and mechanism of a eukaryotic transmembrane ascorbate-dependent oxidoreductase

Structure and mechanism of a eukaryotic transmembrane ascorbate-dependent oxidoreductase

Reduction of MDHAR activity in cherry tomato suppresses growth and yield and MDHAR activity is correlated with sugar levels under high light

Role of the NAD(P)H quinone oxidoreductase NQR and the cytochrome b AIR12 in controlling superoxide generation at the plasma membrane

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