Role of hydrophobic interactions in the encounter complex formation of plastocyanin and cytochrome f complex revealed by paramagnetic NMR spectroscopy.
Role of hydrophobic interactions in the encounter complex formation of plastocyanin and cytochrome f complex revealed by paramagnetic NMR spectroscopy.
J Am Chem Soc. 2013 Apr 29;
Authors: Scanu S, Förster J, Ullmann GM, Ubbink M
Abstract
Protein complex formation is thought to be at least a two-step process, in which the active complex is preceded by the formation of an encounter complex. The interactions in the encounter complex are usually dominated by electrostatic forces, whereas the active complex is also stabilized by non-covalent short range forces. Here, the complex of cytochrome f and plastocyanin, electron transfer proteins involved in photosynthesis, was studied using paramagnetic relaxation NMR spectroscopy. Spin labels were attached to cytochrome f and the relaxation enhancements of plastocyanin nuclei were measured, demonstrating that a large part of the cytochrome f surface area is sampled by plastocyanin. In contrast, plastocyanin is always oriented with its hydrophobic patch toward cytochrome f. The complex was visualized using ensemble docking, showing that the encounter complex is stabilized by hydrophobic as well as electrostatic interactions. The results suggest a model of electrostatic pre-orientation before the proteins make contact, followed by the formation of an encounter complex that rapidly leads to electron transfer active conformations by gradual increase of the overlap of non-polar surface areas on cytochrome f and plastocyanin. In this model the distinction between the encounter and active complexes vanishes, at least in the case of electron transfer complexes, which do not require a high degree of specificity.
PMID: 23627316 [PubMed - as supplied by publisher]
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