Role of positive charge of lysine residue on cytochrome c3for electrostatic interaction with hydrogenase

Abstract

Cytochrome c3from Desulfovibrio vulgaris (Miyazaki) is an electron transfer protein containing four hemes per molecule. Its physiological electron transfer partner is the hydrogenase which catalyzes reversible oxidation of hydrogen. The complex formation between cytochrome c3and hydrogenase is caused by electrostatic interaction, because cytochrome c3is a basic protein and hydrogenase is an acidic protein. As cytochrome c3has 20 lysine residues among 108 amino acids, the positive charges of some lysine residues may play an important role in the interaction with hydrogenase. To clarify the role of positive charge of lysine residue, the positive charge was changed to neutral or negative charge using chemical modification and site-directed mutagenesis. When the positive charges around heme IV were changed, the hydrogen evolution rate with hydrogenase decreased. The affinity between hydrogenase and mutated cytochrome c3(K57Q, K57E, K72Q, K94Q, K94E) were not affected. On the other hand, the affinity of K72E cytochrome c3for hydrogenase was very low. These results suggest that the positive charge around heme IV plays an important role in the electrostatic interaction with hydrogenase in hydrogen evolution.