Abstract
Ferredoxin (Fd) is a soluble electron carrier protein and donates electrons to various Fd-dependent enzymes by forming an electron transfer complex with each enzyme. One of such enzymes is sulfite reductase (SiR) and NMR study of Fd was performed to investigate the interaction sites on Fd with SiR. Upon complex formation with SiR chemical shift changes of 15N labeled Fd were observed mainly on two regions of negatively charged surface. The importance of these regions for the interaction was confirmed by site-directed mutagenesis of Fd. The interaction sites of SiR were also investigated by the enzymatic assay and NMR measurement of various SiR mutants with certain basic residues substituted. One of our important findings is that the interacting sites of Fd for SiR are significantly different from those for Fd:NADP+ reductase, indicative of a combination-specific protein-protein recognition between Fd and each enzyme.
