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Dr. Dror Noy Bioenergetics and Protein Design laboratory

9 May, 2016

Aromatic ring deformation has long been postulated as a mechanism for tuning the absorption spectra of chlorophylls in their natural protein environment.

Dror Noy's lab provided the first direct demonstration of such a mechanism in the water-soluble chlorophyll binding protein (WSCP) from Brassicaceae. Their work is published in and highlighted on the cover of Angewandte Chemie International Edition (10.1002/anie.201512001).

The ability to tune the light-absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light-harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein–pigment interactions that underlie the spectral-tuning mechanisms. We used a novel method for assembling chlorophylls with recombinant water soluble chlorophyll binding proteins (WSCPs), and solved the structure of a type IIa water-soluble chlorophyll binding proteins from cauliflower (CaWSCP). Analysis of the structure revealed a unique mechanism for tuning the spectral properties of chlorophylls in proteins. By comparing the molecular structures of CaWSCP (PDB Id: 5HPZ) to that of type IIb WSCP from Virginia pepperweed (PDB ID: 2DRE), we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by moving a nearby tryptophan residue as a result of changing its hydrogen bonding network. We show by a set of reciprocal point mutations that changing a single amino acid residue accounts for up to 2/3 of the observed spectral shift between the two natural variants.

 Dr. Dror Noy Bioenergetics and Protein Design laboratory

http://onlinelibrary.wiley.com/doi/10.1002/anie.201512001/abstract

 

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