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Aimee M. Terauchi, Shu-Fen Lu,
Mirko Zaffagnini,
Shane Tappa,
Masakazu Hirasawa,
Jatindra N. Tripathy,
David B. Knaff,
Patrick J. Farmer,
Stéphane D. Lemaire,
Toshiharu Hase,
Sabeeha S. Merchant
[show abstract]
[hide abstract]
ABSTRACT: Ferredoxin (Fd) is the major iron-containing protein in photosynthetic organisms and is central to reductive metabolism in
the chloroplast. The Chlamydomonas reinhardtii genome encodes six plant type [Fe2S2] ferredoxins, products of PETF, FDX2–FDX6. We performed the functional analysis of these ferredoxins by localizing Fd, Fdx2, Fdx3, and Fdx6 to the chloroplast by using
isoform-specific antibodies and monitoring the pattern of gene expression by iron and copper nutrition, nitrogen source, and
hydrogen peroxide stress. In addition, we also measured the midpoint redox potentials of Fd and Fdx2 and determined the kinetic
parameters of their reactions with several ferredoxin-interacting proteins, namely nitrite reductase, Fd:NADP+ oxidoreductase, and Fd:thioredoxin reductase. We found that each of the FDX genes is differently regulated in response to changes in nutrient supply. Moreover, we show that Fdx2 (Em = −321 mV), whose expression is regulated by nitrate, is a more efficient electron donor to nitrite reductase relative to
Fd. Overall, the results suggest that each ferredoxin isoform has substrate specificity and that the presence of multiple
ferredoxin isoforms allows for the allocation of reducing power to specific metabolic pathways in the chloroplast under various
growth conditions.
Journal of Biological Chemistry 09/2009; 284(38):25867-25878. · 4.77 Impact Factor
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Aimee M Terauchi, Shu-Fen Lu,
Mirko Zaffagnini,
Shane Tappa,
Masakazu Hirasawa,
Jatindra N Tripathy,
David B Knaff,
Patrick J Farmer,
Stéphane D Lemaire,
Toshiharu Hase,
Sabeeha S Merchant
[show abstract]
[hide abstract]
ABSTRACT: Ferredoxin (Fd) is the major iron-containing protein in photosynthetic organisms and is central to reductive metabolism in the chloroplast. The Chlamydomonas reinhardtii genome encodes six plant type [Fe2S2] ferredoxins, products of PETF, FDX2-FDX6. We performed the functional analysis of these ferredoxins by localizing Fd, Fdx2, Fdx3, and Fdx6 to the chloroplast by using isoform-specific antibodies and monitoring the pattern of gene expression by iron and copper nutrition, nitrogen source, and hydrogen peroxide stress. In addition, we also measured the midpoint redox potentials of Fd and Fdx2 and determined the kinetic parameters of their reactions with several ferredoxin-interacting proteins, namely nitrite reductase, Fd:NADP+ oxidoreductase, and Fd:thioredoxin reductase. We found that each of the FDX genes is differently regulated in response to changes in nutrient supply. Moreover, we show that Fdx2 (Em = -321 mV), whose expression is regulated by nitrate, is a more efficient electron donor to nitrite reductase relative to Fd. Overall, the results suggest that each ferredoxin isoform has substrate specificity and that the presence of multiple ferredoxin isoforms allows for the allocation of reducing power to specific metabolic pathways in the chloroplast under various growth conditions.
Journal of Biological Chemistry 08/2009; 284(38):25867-78. · 4.77 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Two unlinked genes FER1 and FER2 encoding ferritin subunits were identified in the Chlamydomonas genome. An improved FER2 gene model, built on the basis of manual sequencing and incorporation of unplaced reads, indicated 49% identity between the ferritin subunits. Both FER1 and FER2 transcripts are increased in abundance as iron nutrition is decreased but the pattern for each gene is distinct. Using subunit-specific antibodies, we monitored expression at the protein level. In response to low iron, ferritin1 subunits and the ferritin1 complex are increased in parallel to the increase in FER1 mRNA. Nevertheless, the iron content of the ferritin1 complex is decreased. This suggests that increased expression results in increased capacity for iron binding in the chloroplast of iron-limited cells, which supports a role for ferritin1 as an iron buffer. On the other hand, ferritin2 abundance is decreased in iron-deprived cells, indicative of the operation of iron-nutrition-responsive regulation at the translational or post-translational level for FER2. Both ferritin subunits are plastid localized but ferritin1 is quantitatively recovered in soluble extracts of cells while ferritin2 is found in the particulate fraction. Partial purification of the ferritin1 complex indicates that the two ferritins are associated in distinct complexes and do not coassemble. The ratio of ferritin1 to ferritin2 is 70:1 in iron-replete cells, suggestive of a more dominant role of ferritin1 in iron homeostasis. The Volvox genome contains orthologs of each FER gene, indicating that the duplication of FER genes and potential diversification of function occurred prior to the divergence of species in the Volvocales.
Genetics 06/2008; 179(1):137-47. · 4.01 Impact Factor
