Folding and Pigment Binding of Light-Harvesting Chlorophyll a/b Protein (LHCIIb)

Abstract

The major light-harvesting chlorophyll a/b protein (LHCIIb) is one of the most abundant proteins of the chloroplast in green plants. It contains roughly half of the chlorophylls involved in photosynthesis, and exhibits an unusual ability to self-organize in vitro. Simply mixing the apoprotein, native or recombinant, with its pigments, chlorophyll a, chlorophyll b, and xanthophylls, in detergent solution, suffices to trigger protein folding and the assembly of about 18 pigments in their correct binding sites. A study of the mechanism of this self-organization seems worthwhile since (1) our knowledge about membrane protein folding is scarce compared to what we know about the folding of water-soluble proteins, (2) the mechanism of LHCIIb formation in vitro may give useful clues about the so-far unknown pathway of its assembly in the chloroplast, and (3) a thorough understanding of the process may facilitate the application of recombinant LHCIIb in hybrid constructs such as photovoltaic devices or the construction of potentially useful proteins or other polymers that spontaneously bind other dyes at a similarly high density.