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The Influence of Protein-Protein Interactions on the Organization of Proteins within Thylakoid Membranes

I. G. Tremmel ^* , E. Weis  and G. D. Farquhar ^*

^* Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, Australia; and Institut für Botanik, Westfälische Wilhelms-Universität Münster, Münster, Germany

Correspondence: Address reprint requests to Ira Tremmel, E-mail: ira{at}germanynet.de.

The influence of attractive protein-protein interactions on the organization of photosynthetic proteins within the thylakoid membrane was investigated. Protein-protein interactions were simulated using Monte Carlo techniques and the influence of different interaction energies was examined. It was found that weak interactions led to protein clusters whereas strong interactions led to ramified chains. An optimum curve for the relationship between interaction energy and the number of contact sites emerged. With increasing particle densities the effect decreased. In a mixture of interacting and noninteracting particles the distance between the noninteracting particles was increased and there seemed to be much more free space around them. In thylakoids, this could lead to a more homogeneous distribution of the noninteracting but rate-limiting cytochrome bf complexes. Due to the increased free space between cytochrome bf, obstruction of binding sites—occurring unavoidably in a random distribution—may be drastically reduced. Furthermore, protein-protein interactions in thylakoids may lead to a decrease in plastoquinone diffusion.