Fine tuning of chlorophyll spectra by protein-induced ring deformation
Dominika Bednarczyk, Orly Dym, Vadivel Prabahar, and Dror Noy [1]
Molecular Tour
The ability to tune the light absorption properties of chlorophylls by their protein environment is the key to the high efficiency, robustness, and adaptability 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 and to quantify their effect on a pigment’s spectral properties. Here we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants.
We constructed, purified, and solved the crystal structure of water soluble chlorophyll binding protein from cauliflower complex with chlorophyll (CaWSCP-Chl). . Chains A, B, C, and D are coloured purple, pink, grey, and blue. Chlorophylls are shown in ball-and-stick representation with carbons in cyan colour.
