Biochemical properties of the PsbS subunit of photosystem II either purified from chloroplast or recombinant.
The biochemical properties of PsbS protein, a nuclear-encoded Photosystem II subunit involved in the high energy quenching of chlorophyll fluorescence, have been studied using preparations purified from chloroplasts or obtained by overexpression in bacteria. Despite the homology with chlorophyll a/b/xanthophyll-binding proteins of the Lhc family, native PsbS protein does not show any detectable ability to bind chlorophylls or carotenoids in conditions in which Lhc proteins maintain full pigment binding. The recombinant protein, when refolded in vitro in the presence of purified pigments, neither binds chlorophylls nor xanthophylls, differently from the homologous proteins LHCII, CP26, and CP29 that refold into stable pigment-binding complexes. Thus, it is concluded that if PsbS is a pigment-binding protein in vivo, the binding mechanism must be different from that present in other Lhc proteins. Primary sequence analysis provides evidence for homology of PsbS helices I and III with the central 2-fold symmetric core of chlorophyll a/b-binding proteins. Moreover, a structural homology owed to the presence of acidic residues in each of the two lumen-exposed loops is found with the dicyclohexylcarbodiimide/Ca(2+)-binding domain of CP29. Consistently, both native and recombinant PsbS proteins showed [(14)C]dicyclohexylcarbodiimide binding, thus supporting a functional basis for its homology with CP29 on the lumen-exposed loops. This domain is suggested to be involved in sensing low luminal pH.
Dominici
Paola
P
Dipartimento Scientifico e Tecnologico, Università degli Studi di Verona, 37134 Verona, Italy.
Caffarri
Stefano
S
Armenante
Franca
F
Ceoldo
Stefania
S
Crimi
Massimo
M
Bassi
Roberto
R
D000595:Amino Acid Sequence; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D061146:Chlorophyll Binding Proteins; D002736:Chloroplasts / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D003902:Detergents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007477:Ions; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D018724:Spinacia oleracea / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism
C069660:CP29 light harvesting complex; D061146:Chlorophyll Binding Proteins; D003902:Detergents; D007477:Ions; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011994:Recombinant Proteins