The neoxanthin binding site of the major light harvesting complex (LHCII) from higher plants

The localisation of the xanthophyll neoxanthin within the structure of the major light harvesting complex (LHCII) of higher plants has been investigat ed by site-directed mutagenesis and spectroscopic methods. Mutation analysi s performed on pigment binding sites in different helix domains leads to se lective loss of neoxanthin for mutations on helix C thus localising this pi gment between the helix C and helix A/B domains. Recombinant proteins bindi ng two lutein molecules per polypeptide but lacking neoxanthin have been us ed in order to determine the contribution of neoxanthin to the absorption a nd linear dichroism spectra. The data were used to derive the orientation o f the neoxanthin transition moment, lying in the polyene chain, which was t hus determined to form an angle of 57 +/- 1.5 degrees with respect to the n ormal to the membrane plane where the protein is inserted. On the basis of these results we propose a model for the localisation of the carotenoid sit e in the LHCII structure which is still unresolved. (C) 1999 Federation of European Biochemical Societies.