title: A new structural insight into differential interaction of cyanobacterial and plant ferredoxins with nitrite reductase as revealed by NMR and X-ray crystallographic studies.
abstract: Ferredoxin (Fd), which plays a pivotal role in photosynthesis as an electron carrier, forms a transient complex with various Fd-dependent enzymes, such as nitrite reductase (NiR), to achieve efficient intermolecular electron transfer. We studied the protein-protein interaction of Fd and NiR by NMR spectroscopy and determined three acidic regions of Fd to be major sites for the interaction with NiR, indicating that the complex is stabilized through electrostatic interaction. During this study, we found Fds from higher plant and cyanobacterium, in spite of their high structural similarities including the above acidic regions, differ remarkably in the interaction with cyanobacterial NiR. In activity assay of NiR, K(m) value for maize Fd (74.6 µM) was 9.6 times larger than that for Leptolyngbya boryana Fd (7.8 µM). The two Fds also showed a similar difference in binding assay to NiR-immobilized resin. Comparative site-specific mutagenesis of two Fds revealed that their discriminative ability for the interaction with NiR is attributed mainly to non-charged residues in the peripheral region of [2Fe-2S] cluster. These non-charged residues are conserved separately between Fds of plant and cyanobacterial origins. Our data highlight that intermolecular force(s) other than electrostatic attraction is(are) also crucial for the molecular interaction between Fd and partner enzyme.
authors.affiliation: Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan. enzyme@protein.osaka-u.ac.jp
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Sakakibara
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kimura
authors.forename: Akira
authors.initials: A
authors.lastname: Iwamura
authors.forename: Takashi
authors.initials: T
authors.lastname: Saitoh
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikegami
authors.forename: Genji
authors.initials: G
authors.lastname: Kurisu
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Hase
mesh_terms: D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry* / Q000201:enzymology; D005288:Ferredoxins / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D003313:Zea mays / Q000737:chemistry*
chemical_list: D005288:Ferredoxins; D009572:Nitrite Reductases