Origin of the far-red absorbance in eustigmatophyte algae red-shifted Violaxanthin-ChlorophyllaProtein

Abstract

AbstractPhotosynthetic organisms harvest light for energy. Some eukaryotic algae have specialized in harvesting far-red light by tuning chlorophyllaabsorption through a mechanism still to be elucidated. Here, we combined optically detected magnetic resonance and pulsed electron paramagnetic resonance measurements on red-adapted light-harvesting complexes, rVCP, isolated from the freshwater eustigmatophyte algaTrachydiscus minutusto identify the location of the pigments responsible for this remarkable adaptation. The pigments have been found to belong to an excitonic cluster of chlorophyllsaat the core of the complex, close to the central carotenoids in L1/L2 sites. A pair of structural features of the Chla403/a603 binding site, namely the histidine-to-asparagine substitution in the magnesium-ligation residue and the small size of the amino acid at thei-4 position, are proposed to be the origin of this trait. Phylogenetic analysis of various eukaryotic red antennae identified several potential LHCs that could share this tuning mechanism.