Reconstitution and pigment-binding properties of recombinant CP29

Abstract

The minor light-harvesting chlorophyll-a/b-binding protein CP29 (Lhcb4), overexpressed in Escherichia coli, has been reconstituted in vitro with pigments. The recombinant pigment-protein complexes show biochemical and spectral properties identical to the native CP29 purified from maize thylakoids. The xanthophyll lutein is the only carotenoid necessary for reconstitution, a finding consistent with the structural role of two lutein molecules/polypeptide suggested by the crystallographic data for the homologous protein light-harvesting chlorophyll-a/b-binding protein of photosystem II (LHCII). The CP29 protein scaffold can accommodate different chromophores. This conclusion was deduced by the observation that the pigment composition of the reconstituted protein depends on the pigments present in the reconstitution mixture. Thus, in addition to a recombinant CP29 identical to the native one, two additional forms of the complex could be obtained by increasing chlorophyll b content. This finding is typical of CP29 because the major LHCII complex shows an absolute selectivity for chromophore binding [Plumley, F. G. & Schmidt, G. W. (1987) Proc. Natl Acad. Sci. USA 84, 146-150; Paulsen, H., Rümler, U. & Rüdiger, W. (1990) Planta (Heidelb.) 181, 204-211], and it is consistent with the higher stability of CP29 during greening and in chlorophyll b mutants compared with LHCII.