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Determination of relative chlorophyll binding affinities in the major light-harvesting chlorophyll a/b complex

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Fey,  Holger
Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Hobe, S., Fey, H., Rogl, H., & Paulsen, H. (2003). Determination of relative chlorophyll binding affinities in the major light-harvesting chlorophyll a/b complex. The Journal of Biological Chemistry, 278, 5912-5919. doi:10.1074/jbc.M211145200.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-DB51-D
Abstract
The major light-harvesting complex (LHCIIb) of photosystem II can be reconstituted in vitro from its recombinant apoprotein in the presence of a mixture of carotenoids and chlorophylls a and b. By varying the chlorophyll a/b ratio in the reconstitution mixture, the relative amounts of chlorophyll a and chlorophyll b bound to LHCIIb can be changed. We have analyzed the chlorophyll stoichiometry in recombinant wild type and mutant LHCIIb reconstituted at different chlorophyll a/b ratios in order to assess relative affinities of the chlorophyll-binding sites. This approach reveals five sites that exclusively bind chlorophyll b. Another site exhibits a slight preference of chlorophyll b over chlorophyll a. The remaining six sites are filled preferentially with chlorophyll a but also tolerate chlorophyll b when this is offered at a large excess. Three of these chlorophyll a-affine sites could be assigned to distinct positions defined by the three-dimensional LHCIIb structure. Exclusive chlorophyll b sites complemented by chlorophyll a sites that are selective only to a certain extent are consistent with the observation that chlorophyll b but not chlorophyll a is essential for reconstituting stable LHCIIb. These data offer an explanation why a rather constant chlorophyll a/b ratio is observed in native LHCIIb despite the apparent promiscuity of some binding sites.