A brownian dynamics study of evolotionary cahnges in electrostatic interactions between plastocyanin and cytochrome f in cyanobacteria and plants.

Abstract

Brownian Dynamics (BD) were used to model the electrostatic interactions of Phormidium plastocyanin cytochrome f (cyt f) with Phormidium and Prochlorothrix plastocyanin (PC) in order to explore evolutionary relationships with proteins from higher plants such as poplar (Pearson and Gross, Biophys. J. 75: 2698-2711 (1998) and spinach. Cyt f¿s from higher plants such as turnip typically contain five conserved positively charged residues (#58, #65, #66, #189 and #209) that produces a positively-charged electrostatic field which attracts negatively-charged residues on PC (positions #42-45 and #59-61). In Phormidium cyt f, all but residues #66 is replaced by a negatively-charged residue For Phormidium PC, #44 and #45. are the only negative charges that remain and a Zn2+ ion lies adjacent to these residues in the crystal structure. All cyanobacterial PC contain an arginine at position #86 replacing a glutamine in other PC¿s. BD simulations of Phormdiium PC with Phormidium cyt f show a significant number of "close complexes" formed in the presence of the Zn2+ ion compared to almost none in its absence suggesting that a divalent cation may occupy that position in vivo.. A greater number of close complexes was observed using Prochlorothrix PC. Replacing Tyr 12 with a glycine (found in all other PC¿s) decreased the Cu-Fe distance for maximal complex formation due to a decrease in steric hindrance. In conclusion, electrostatic interactions occur between PC and cyt f in all species but the signs of the electrostatic fields are reversed in cyanobacteria.