Crystal structures of a novel ferric reductase from the hyperthermophilic archaeon Archaeoglobus fulgidus and its complex with NADP(+)

Hj. Chiu et al., Crystal structures of a novel ferric reductase from the hyperthermophilic archaeon Archaeoglobus fulgidus and its complex with NADP(+), STRUCTURE, 9(4), 2001, pp. 311-319
Citations number
Categorie Soggetti
Biochemistry & Biophysics
Journal title
ISSN journal
0969-2126 → ACNP
Year of publication
311 - 319
SICI code
Background: Studies performed within the last decade have indicated that mi crobial reduction of Fe(III) to Fe(II) is a biologically significant proces s. The ferric reductase (FeR) from Archaeoglobus fulgidus is the first repo rted archaeal ferric reductase and it catalyzes the flavin-mediated reducti on of ferric iron complexes using NAD(P)H as the electron donor. Based on i ts catalytic activity, the A. fulgidus FeR resembles the bacterial and euka ryotic assimilatory type of ferric reductases. However, the high cellular a bundance of the A. fulgidus FeR (similar to0.75% of the total soluble prote in) suggests a catabolic role for this enzyme as the terminal electron acce ptor in a ferric iron-based respiratory pathway [1]. Results: The crystal structure of recombinant A. fulgidus FeR containing a bound FMN has been solved at 1.5 Angstrom resolution by multiple isomorphou s replacement/anomalous diffraction (MIRAS) phasing methods, and the NADP()- bound complex of FeR was subsequently determined at 1.65 Angstrom resolu tion. FeR consists of a dimer of two identical subunits, although only one subunit has been observed to bind the redox cofactors. Each subunit is orga nized around a six-stranded antiparallel beta barrel that is homologous to the FMN binding protein from Desulfovibrio vulgaris. This fold has been sho wn to be related to a circularly permuted Version of the flavin binding dom ain of the ferredoxin reductase superfamily. The A. fulgidus ferric reducta se is further distinguished from the ferredoxin reductase superfamily by th e absence of a Rossmann fold domain that is used to bind the NAD(P)H. Inste ad, FeR uses its single domain to provide both the flavin and the NAD(P)H b inding sites. Potential binding sites for ferric iron complexes are identif ied near the cofactor binding sites. Conclusions: The work described here details the structures of the enzyme-F MN, enzyme-FMN-NADP(+), and possibly the enzyme-FMN-iron intermediates that are present during the reaction mechanism. This structural information hel ps identify roles for specific residues during the reduction of ferric iron complexes by the A. fulgidus FeR.