X-ray structure of the high-salt form of the peridinin-chlorophyll a-protein from the dinoflagellate Amphidinium carterae: modulation of the spectral properties of pigments by the protein environment.
Light-harvesting complexes have evolved into very different structures but fulfill the same function, efficient harvesting of solar energy. In these complexes, pigments are fine-tuned and properly arranged to gather incoming photons. In the photosynthetic dinoflagellate Amphidinium carterae, two variants of the soluble light-harvesting complex PCP have been found [main form PCP (MFPCP) and high-salt PCP (HSPCP)], which show small variations in their pigment arrangement and tuning mechanisms. This feature makes them ideal models for studying pigment-protein interactions. Here we present the X-ray structure of the monomeric HSPCP determined at 2.1 A resolution and compare it to the structure of trimeric MFPCP. Despite the high degree of structural similarity (rmsd C(alpha)-C(alpha) of 1.89 A), the sequence variations lead to a changed overall pigment composition which includes the loss of two carotenoid molecules and a dramatic rearrangement of the chlorophyll phytol chains and of internal lipid molecules. On the basis of a detailed structural comparison, we favor a macrocycle geometry distortion of the chlorophylls rather than an electrostatic effect to explain energetic splitting of the chlorophyll a Q(y) bands [Ilagan, R. P. (2006) Biochemistry 45, 14052-14063]. Our analysis supports their assignment of peridinin 611* as the single blue-shifted peridinin in HSPCP but also highlights another electrostatic feature due to glutamate 202 which could add to the observed binding site asymmetry of the 611*/621* peridinin pair.
Schulte
Tim
T
Biophysics, Department of Biology and Biotechnology, Ruhr-University Bochum, D-44780 Bochum, Germany.
Sharples
Frank P
FP
Hiller
Roger G
RG
Hofmann
Eckhard
E
D000818:Animals; D001665:Binding Sites; D002338:Carotenoids / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004141:Dinoflagellida / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism*; D012492:Salts / Q000378:metabolism*; D013057:Spectrum Analysis; D055672:Static Electricity
D015800:Protozoan Proteins; D012492:Salts; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002338:Carotenoids