Tyrosine 64 of cytochrome c553 is required for electron exchange with formate dehydrogenase in Desulfovibrio vulgaris Hildenborough

Replacement of tyrosine 64 by alanine in cytochrome c553 from Desulfovibrio vulgarisHildenborough prevents electron transfer with the formate dehydrogenase. Biophysical and biochemical studies show that the protein is correctly folded and that the oxidoreduction potential is not modified. The solution structure of the mutant cytochrome determined by two-dimensional (2D) NMR clearly establishes that the overall fold of the molecule is nearly identical to that of the wild-type cytochrome. The electrostatic surface charge distributions for the wild-type and mutant cytochrome are similar, suggesting that the interaction site of the physiological partners is not modified by the mutation. The lack of the aromatic ring induces slight destabilization of the hydrophobic core of the molecule and modifications of the hydrogen bond at position 64, as well as conformational disorder of the side chain of K63. The loss of the hydrogen bond from tyrosine 64 and the increase of the solvent exposure of the heme are probably responsible of the loss of electron transfer between formate dehydrogenase and cytochrome c553.