PIGMENT-BINDING PROPERTIES OF THE RECOMBINANT PHOTOSYSTEM-II SUBUNIT CP26 RECONSTITUTED IN-VITRO

CP26 is the most recently described antenna protein in higher plants w hich has been reported to be involved in xanthophyll-dependent regulat ion of the light-harvesting function but is largely unknown due to the difficulties of purification. In this study we have overexpressed in Escherichia coil the Lhcb5 gene product and reconstituted CP26 in vitr o by refolding the recombinant protein in the presence of chlorophyll a, chlorophyll b and xanthophylls. The resulting pigment-protein compl ex is stable enough to be isolated by partially denaturing gel electro phoresis. Reconstitution and isolation conditions for CP26 are similar to those used for other chlorophyll alb complexes like the major ligh t-harvesting complex of photosystem II (LHCII) and CP29; however, CP26 differs with regard to its lower specificity in carotenoid binding. M ost significantly, rather stable recombinant CP26 can be reconstituted containing violaxanthin as the only carotenoid. This enhanced plastic ity with respect to carotenoid binding is consistent with CP26 being t he major binding protein of violaxanthin involved in the xanthophyll c ycle. The availability of recombinant CP26 opens the way to a better c haracterisation of this pigment-protein complex with regard to its bio chemistry and its physiological functions.