1ddi
From Proteopedia
|
CRYSTAL STRUCTURE OF SIR-FP60
Overview
Escherichia coli NADPH-sulfite reductase (SiR) is a 780 kDa multimeric, hemoflavoprotein composed of eight alpha-subunits (SiR-FP) and four, beta-subunits (SiR-HP) that catalyses the six electron reduction of, sulfite to sulfide. Each beta-subunit contains a Fe4S4 cluster and a, siroheme, and each alpha-subunit binds one FAD and one FMN as prosthetic, groups. The FAD gets electrons from NADPH, and the FMN transfers the, electrons to the metal centers of the beta-subunit for sulfite reduction., We report here the 1.94 A X-ray structure of SiR-FP60, a recombinant, monomeric fragment of SiR-FP that binds both FAD and FMN and retains the, catalytic properties of the native protein. The structure can be divided, into three domains. The carboxy-terminal part of the enzyme is composed of, an antiparallel beta-barrel which binds the FAD, and a variant of the, classical pyridine dinucleotide binding fold which binds NADPH. These two, domains form the canonic FNR-like module, typical of the ferredoxin NADP+, reductase family. By analogy with the structure of the cytochrome P450, reductase, the third domain, composed of seven alpha-helices, is supposed, to connect the FNR-like module to the N-terminal flavodoxine-like module., In four different crystal forms, the FMN-binding module is absent from, electron density maps, although mass spectroscopy, amino acid sequencing, and activity experiments carried out on dissolved crystals indicate that a, functional module is present in the protein. Our results clearly indicate, that the interaction between the FNR-like and the FMN-like modules, displays lower affinity than in the case of cytochrome P450 reductase. The, flexibility of the FMN-binding domain may be related, as observed in the, case of cytochrome bc1, to a domain reorganisation in the course of, electron transfer. Thus, a movement of the FMN-binding domain relative to, the rest of the enzyme may be a requirement for its optimal positioning, relative to both the FNR-like module and the beta-subunit.
About this Structure
1DDI is a Single protein structure of sequence from Escherichia coli with FAD and NAP as ligands. Active as Sulfite reductase (NADPH), with EC number 1.8.1.2 Full crystallographic information is available from OCA.
Reference
Four crystal structures of the 60 kDa flavoprotein monomer of the sulfite reductase indicate a disordered flavodoxin-like module., Gruez A, Pignol D, Zeghouf M, Coves J, Fontecave M, Ferrer JL, Fontecilla-Camps JC, J Mol Biol. 2000 May 26;299(1):199-212. PMID:10860732
Page seeded by OCA on Tue Nov 20 13:11:43 2007
