Spectroscopic and electrochemical studies on structural change of plastocyanin and its tyrosine 83 mutants induced by interaction with lysine peptides

Interactions of wild-type and Tyr83 mutant (Y83F, Y83S, Y83L, and Y83H) plastocyanins (PCs) with lysine peptides as models for the PC interacting site of cytochrome f have been studied by absorption, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopies and electrochemical measurements. The spectral and electrochemical properties of PCs corresponded well with each other; species having a longer wavelength maximum for the S(Cys) π → Cu 3d(x²-y²) charge transfer (CT) band observed around 600 nm and a stronger intensity for the 460-nm absorption band exhibited stronger intensities for the positive Met → Cu 3d(x²-y²) and negative His π → Cu 3d(x²-y²) circular dichroism (CD) bands at about 420 and 470 nm, respectively, a lower average v(Cu-S) frequency, a smaller |A(is parallel with)| EPR parameter, and a higher redox potential, properties all related to a weaker Cu-S(Cys) bond and a more tetrahedral planar geometry for the Cu site. Similarly, on oligolysine binding to wild-type and several Tyr83 mutant PCs, a longer absorption maximum for the 600-nm CT band, a stronger intensity for the 460-nm absorption band, stronger 420-nm positive and 470-nm negative CD bands, and a lower average v(Cu-S) frequency were observed, suggesting that PC assumes a slight more tetrahedral geometry on binding of oligolysine. Since changes were observed for both wild-type and Tyr83 mutant PCs, the structural change due to binding of oligolysine to PC may not be transmitted through the path of Tyr83-Cys84-copper by a cation-π interaction which is proposed for electron transfer.