A Post Genomic Characterization of Arabidopsis Ferredoxins

Abstract

In higher plant plastids, ferredoxin (Fd) is the unique soluble electron carrier protein located in the stroma. Consequently, a wide variety of essential metabolic and signaling processes depend upon reduction by Fd. The currently available plant genomes of Arabidopsis and rice (Oryza sativa) contain several genes encoding putative Fds, although little is known about the proteins themselves. To establish whether this variety represents redundancy or specialized function, we have recombinantly expressed and purified the four conventional [2Fe-2S] Fd proteins encoded in the Arabidopsis genome and analyzed their physical and functional properties. Two proteins are leaf type Fds, having relatively low redox potentials and supporting a higher photosynthetic activity. One protein is a root type Fd, being more efficiently reduced under nonphotosynthetic conditions and supporting a higher activity of sulfite reduction. A further Fd has a remarkably positive redox potential and so, although redox active, is limited in redox partners to which it can donate electrons. Immunological analysis indicates that all four proteins are expressed in mature leaves. This holistic view demonstrates how varied and essential soluble electron transfer functions in higher plants are fulfilled through a diversity of Fd proteins.Ferredoxin (Fd) is a soluble, low M r protein that mediates transfer of one electron from a donor to an acceptor. The redox active center is a [2Fe-2S] cluster that confers a highly negative redox potential on the protein (Ϫ350 to Ϫ450 mV), making Fd a powerful reductant. The [2Fe-2S] cluster is ligated by four highly conserved Cys residues.A broad spectrum of redox metabolism in higher plant plastids involves Fd. Although the name Fd was first used to describe a non-photosynthetic bacterial protein involved in nitrogen fixation (Mortenson et al., 1962), Fd is best known for a photosynthetic role: accepting electrons from photosystem I (PSI) and donating them to the enzyme Fd:NADP ϩ oxidoreductase (FNR) for photoreduction of NADP ϩ (Arnon, 1989). Donation of electrons by Fd has now been demonstrated to many other plastid enzymes essential for cellular processes, including nitrogen assimilation (nitrite reductase), sulfur assimilation (sulfite reductase [SiR]), amino acid synthesis (Glnoxoglutarate amino transferase), fatty acid synthesis (fatty acid desaturase), and redox regulation (Fd: thioredoxin reductase) (Knaff, 1996). In addition to PSI, Fd may be reduced by NADPH oxidation in a reversal of the FNR reaction (Suzuki et al., 1985). This enables Fd-dependent metabolism to continue under non-photosynthetic conditions, such as in root plastids.Fds are present as multiple isoforms in many plants and algae (Bertini et al., 2002). In higher plants, those predominantly expressed in photosynthetic tissues can be crudely divided from those that are not on the basis of primary sequence (Wada et al., 1986). Work using maize (Zea mays) has exposed functional differences between these Fd types; the rate of light-dependent NA...

Nicotiana tabacum Tsip1-Interacting Ferredoxin 1 Affects Biotic and Abiotic Stress Resistance

“…Plant chloroplasts have ferredoxins (Fds) that participate in electron flow in the chloroplast by receiving and donating electrons (Fukuyama, 2004;Hanke et al, 2004). Identified NtTfd1 also contained a putative single iron-sulfur cluster (Fe 2 S 2 ) domain and catalytic loops that are conserved among all Fd proteins (Fig.…”

“…Reduced Fd reduces either thioredoxin via Fd:thioredoxin reductase or NADP via Fd:NADP reductase (Fukuyama, 2004;Hanke et al, 2004). Furthermore, reduced Fd donates the electrons to other metabolic pathways by interacting with various enzymes in the chloroplast (Knaff and Hirasawa, 1991;Kurisu et al, 2001) although Fd also functions in nonphotosynthetic cells like root tissues (Terauchi et al, 2009).…”

Glutamine Synthetase-Glutamate Synthase Pathway and Glutamate Dehydrogenase Play Distinct Roles in the Sink-Source Nitrogen Cycle in Tobacco

“…NADPH serves as the primary reductant for Glu formation via the reversed reaction of photosystem-dependent Fd:NADP 1 oxidoreductase (EC 1.18.1.2; Fig. 5; Hanke et al, 2004;Feraud et al, 2005). Taken together, the data support the notion that the GS-GOGAT cycle takes place in vascular cells for the biosynthesis of Glu and Gln prior to the cycle of amino acids, and that GDH does not play a role in Glu supply even in old leaves of tobacco where GDH is induced.…”

N-Terminal Structure of Maize Ferredoxin:NADP+ Reductase Determines Recruitment into Different Thylakoid Membrane Complexes

“…Extracts were desalted and detergent removed over Sephadex-G50. Ferredoxin-dependent electron transfer from NADPH to cytochrome c was measured in 100 µg total protein, basically as described previously (Hanke et al, 2004), in 50 mM HEPES-NaOH, pH 7.5, 100 mM NaCl, 200 µM NADPH, and 200 µM cytochrome c with 20 µM Arabidopsis ferredoxin 2.…”