(RW)4-NH2 is a linear cationic peptide, rich in arginine (Arg or R) and tryptophan (Trp or W)  residues. In this study, we investigate the interaction between (RW)4-NH2 and photosystem I (PS I) in the presence of Al3+ and Eu3+ionsusing FTIR, Raman, UV-Visible, and fluorescence techniques. Infrared curve-fitting data indicate that  (RW)4-NH2 adopts a major alpha-helix structure. Upon photosystem I addition, the major alpha-helix structure is retained but a minor random coil structure is induced. The addition of Al3+ and Eu3+ ions to the system (RW)4-NH2/PS I induces a major �-sheet structure and a minor -helix structure. Fluorescence emission and absorption spectra showed a strong interaction between (RW)4-NH2 and photosystem in the presence of Al3+ and Eu3+ ions.  Al3+ ions induced a red shift of the peaks of PS I and the quenching of the fluorescence of PS I, while Eu3+ induces only the quenching of the fluorescence of PS I. Fluorescence spectra suggested that tryptophan residue (W) is the preferred binding site of (RW)4-NH2 to PS I in the presence of metal ions. The formation constants of the complexes were calculated from the fluorescence data using the modified Benesi-Hildebrand equation. In addition, Raman spectra revealed that (RW)4-NH2 interacts with PS I through the O atom of the amide groups

Conformational changes in peptide induced by photosystem I: A spectroscopic study

248th National Meeting (2014)

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