Role of the C-Terminal Tyrosine of Ferredoxin-Nicotinamide Adenine Dinucleotide Phosphate Reductase in the Electron Transfer Processes with Its Protein Partners Ferredoxin and Flavodoxin
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- 作者：Isabel Nogué ; s ; Jesú ; s Tejero ; John K. Hurley ; Darí ; o Paladini ; Susana Frago ; Gordon Tollin ; Stephen G. Mayhew ; Carlos Gó ; mez-Moreno ; Eduardo A. Ceccarelli ; Né ; stor Carri
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：May 25, 2004
- 年：2004
- 卷：43
- 期：20
- 页码：6127 - 6137
- 全文大小：352K
- 年卷期：v.43,no.20(May 25, 2004)
- ISSN：1520-4995
文摘
The catalytic mechanism proposed for ferredoxin-NADP+ reductase (FNR) is initiated byreduction of its flavin adenine dinucleotide (FAD) cofactor by the obligatory one-electron carriers ferredoxin(Fd) or flavodoxin (Fld) in the presence of oxidized nicotinamide adenine dinucleotide phosphate (NADP+).The C-terminal tyrosine of FNR, which stacks onto its flavin ring, modulates the enzyme affinity forNADP+/H, being removed from this stacking position during turnover to allow productive docking of thenicotinamide and hydride transfer. Due to its location at the substrate-binding site, this residue might alsoaffect electron transfer between FNR and its protein partners. We therefore studied the interactions andelectron-transfer properties of FNR proteins mutated at their C-termini. The results obtained with thehomologous reductases from pea and Anabaena PCC7119 indicate that interactions with Fd or Fld arehardly affected by replacement of this tyrosine by tryptophan, phenylalanine, or serine. In contrast, electronexchange is impaired in all mutants, especially in the nonconservative substitutions, without majordifferences between the eukaryotic and the bacterial FNR. Introduction of a serine residue shifts the flavinreduction potential to less negative values, whereas semiquinone stabilization is severely hampered, introducing further constraints to the one-electron-transfer processes. Thus, the C-terminal tyrosine of FNRplays distinct and complementary roles during the catalytic cycle, (i) by lowering the affinity for NADP+/Hto levels compatible with steady-state turnover, (ii) by contributing to the flavin semiquinone stabilizationrequired for electron splitting, and (iii) by modulating the rates of electron exchange with the proteinpartners.