A Brownian Dynamics Study of the Interaction of Phormidium Cytochrome f with Various Cyanobacterial Plastocyanins

¹ The Ohio State University

^* To whom correspondence should be addressed. E-mail: gross.3{at}osu.edu.

Submitted on April 22, 2005
Revised on June 7, 2005
Accepted on 13 September 2005

	Abstract

Brownian Dynamics simulations were used to study the role of electrostatic forces in the interactions of cytochrome f from the cyanobacterium Phormidium laminosum with various cyanobacterial plastocyanins. Both the net charge on the plastocyanin molecule and the charge configuration around H92 (H87 in higher plants) are important in determining the interactions. Those plastocyanins with a net charge more negative than -2.0, including those from Synechococcus sp. PCC7942, Synechocystis, sp. 6803 and Phormidium laminosum showed very little complex formation. On the other hand, complex formation for those with a net charge more positive than -2.0 (including Nostoc sp. PCC7119 and Prochlorothrix hollandica) as well as Nostoc plastocyanin mutants, showed a linear dependence of complex formation upon the net charge on the plastocyanin molecule. Mutation of charged residues on the surface of the PC molecules also affected complex formation. Simulations involving plastocyanin mutants K35A, R93A and K11A (when present) showed inhibition of complex formation. In contrast, D10A and E17A mutants showed an increase in complex formation. All of these residues surround the H92 (H87 in higher plant plastocyanins) ligand to the copper. An examination of the closest electrostatic contacts shows that these residues interact with D63, E123, R157, D188 and the heme on Phormidium cytochrome f. In the complexes formed, the long axis of the PC molecule lies perpendicular to the long axis of cytochrome f. There is considerable heterogeneity in the orientation of plastocyanin in the complexes formed.

Key Words: Brownian dynamics, cyanobacteria, cytochrome f, interactions, plastocyanin