Role of charged amino acid residues of plastocyanin in interaction with cytochrome b$_6$f complex and photosystem i of higher plants: a study using the Brownian dynamics method

Plastocyanin is an electron carrier protein in the electron transport chain of chloroplasts, carrying out the transfer of an electron from cytochrome f of the cytochrome b6f complex to photosystem I. Using the method of Brownian dynamics, the process of formation of the encounter complex of plastocyanin and photosystem I of higher plants was studied. The electrostatic properties of proteins were studied, and the most important amino acid residues for their interaction were identified. It was shown that plastocyanin contacts the positively charged alpha-helix protruding into the lumen of the F subunit of photosystem I with amino acid residues of both its “large” (D42, E43, D44, E45, D51) and “small” (E59, E60, D61) the negatively charged regions in 73% of cases, and only the "large" region in 27% of cases. A comparison of the study results with previously obtained data on the interaction of plastocyanin with cytochrome f made it possible to identify the role of charged amino acid residues of plastocyanin in the process of complex formation with photosystem I and cytochrome f. When interacting with cytochrome f, a positively charged region located near the small domain of cytochrome f and formed by amino acid residues K58, K65, K66, K187 and R209, attracts negatively charged amino acid residues D42, E43, D44, E45, D51 of the “large” region of plastocyanin, forming an electrostatic hinge contact around which rotation occurs when the final complex is formed. The “small” region of plastocyanin is involved in the stabilization of the final complex. Thus, both in the formation of the encounter complex with photosystem I, and in the reaction with cytochrome f the same negatively charged amino acid residues of plastocyanin are used.