Chromophore organization in the higher-plant photosystem II antenna protein CP26.
The chlorophyll a/b-xanthophyll-protein CP26 complex belongs to the Lhc protein family. It binds nine chlorophylls and two xanthophylls per 26.6 kDa polypeptide. Determination of the characteristics of each binding site is needed for the understanding of functional organization of individual proteins belonging to the photosystem II supramolecular complex. The biochemical and spectroscopic features of native CP26 are presented here together with identification of pigment binding and energy transitions in different sites. The analysis has been performed via a new approach using recombinant CP26 complexes in which the chromophore content has been experimentally modified. Data were interpreted on the basis of homology with CP29 and LHCII complexes, for which detailed knowledge is available from mutation analysis. We propose that one additional Chl b is present in CP26 as compared to CP29 and that it is located in site B2. We also found that in CP26 three chlorophyll binding sites are selective for Chl a, one of them being essential for the folding of the pigment-protein complex. Two xanthophyll binding sites were identified, one of which (L1) is essential for protein folding and specifically binds lutein. The second site (L2) has lower selectivity and can bind any of the xanthophyll species present in thylakoids.
Croce
Roberta
R
Dipartimento Scientifico e Tecnologico-Facoltà di Scienze MM.FF.NN., Strada Le Grazie 15, 37134 Verona, Italy.
Canino
Giusy
G
Ros
Francesca
F
Bassi
Roberto
R
D001665:Binding Sites; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D061146:Chlorophyll Binding Proteins; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D011489:Protein Denaturation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D020524:Thylakoids / Q000737:chemistry; D024341:Xanthophylls / Q000737:chemistry / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry
D061146:Chlorophyll Binding Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011994:Recombinant Proteins; D024341:Xanthophylls; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A