Amino acid residues responsible for the different pH dependency of photosynthetic type and non-photosynthetic type ferredoxins in the electron transfer reaction with ferredoxin-NADP+ reductase from maize leaves

Abstract

In higher plants, ferredoxin (Fd) is present as distinct isoproteins of photosynthetic type (LFd) and non-photosynthetic type (RFd), which exhibit differential function despite their similarity in the 3D structures. We previously showed that pH-dependency of electron transfer activity with ferredoxin-NADP+ reductase (FNR) was opposite between LFd and RFd, which was explained by the opposite pH-dependent profile of Km for the two Fds, and that the differences of C-terminal residues and 78th residue between the two Fds were partly responsible for the different pH dependency. In this study, we further investigated the determinants responsible for the different pH dependency between the LFd and RFd. Site-directed mutants of Fd, substituted at the residues on the interface with FNR, were prepared. Kinetic analyses using the single site-directed mutants and their combined, multiple mutants showed that combination of the substitutions of Fd residues at 61, 63, 78th and C-terminal region located at the interface with FNR conferred opposite pH-dependency, which indicated that these residues are the enough determinant for their opposite pH dependency of LFd and RFd in the electron transfer reaction with FNR.