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  • Title: Mechanism of coenzyme recognition and binding revealed by crystal structure analysis of ferredoxin-NADP+ reductase complexed with NADP+.
    Author: Hermoso JA, Mayoral T, Faro M, Gómez-Moreno C, Sanz-Aparicio J, Medina M.
    Journal: J Mol Biol; 2002 Jun 21; 319(5):1133-42. PubMed ID: 12079352.
    Abstract:
    The flavoenzyme ferredoxin-NADP+ reductase (FNR) catalyses the production of NADPH in photosynthesis. The three-dimensional structure of FNR presents two distinct domains, one for binding of the FAD prosthetic group and the other for NADP+ binding. In spite of extensive experiments and different crystallographic approaches, many aspects about how the NADP+ substrate binds to FNR and how the hydride ion is transferred from FAD to NADP+ remain unclear. The structure of an FNR:NADP+ complex from Anabaena has been determined by X-ray diffraction analysis of the cocrystallised units to 2.1 A resolution. Structural perturbation of FNR induced by complex formation produces a narrower cavity in which the 2'-phospho-AMP and pyrophosphate portions of the NADP+ are perfectly bound. In addition, the nicotinamide mononucleotide moiety is placed in a new pocket created near the FAD cofactor with the ribose being in a tight conformation. The crystal structure of this FNR:NADP+ complex obtained by cocrystallisation displays NADP+ in an unusual conformation and can be considered as an intermediate state in the process of coenzyme recognition and binding. Structural analysis and comparison with previously reported complexes allow us to postulate a mechanism which would permit efficient hydride transfer to occur. Besides, this structure gives new insights into the postulated formation of the ferredoxin:FNR:NADP+ ternary complex by prediction of new intermolecular interactions, which could only exist after FNR:NADP+ complex formation. Finally, structural comparison with the members of the broad FNR structural family also provides an explanation for the high specificity exhibited by FNR for NADP+/H versus NAD+/H.
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