Understanding the changes in the circular dichroism of light harvesting complex II upon varying its pigment composition and organization

Georgakopoulou, S. and van der Zwan, G. and Bassi, R. and van Grondelle, R. and van Amerongen, H. and Croce, R.. (2007) Understanding the changes in the circular dichroism of light harvesting complex II upon varying its pigment composition and organization. Biochemistry, Vol. 46, H. 16. pp. 4745-4754.

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Official URL: http://edoc.unibas.ch/dok/A5249173

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In this work we modeled the circular dichroism (CD) spectrum of LHCII, the main light harvesting antenna of photosystem II of higher plants. Excitonic calculations are performed for a monomeric subunit, taken from the crystal structure of trimeric LHCII from spinach [Liu, Z. F., Yan, H. C., Wang, K. B., Kuang, T. Y., Zhang, J. P., Gui, L. L., An, X. M., and Chang, W. R. (2004) Nature 428, 287-292]. All of the major features of the CD spectrum above 450 nm are satisfactorily reproduced, and possible orientations of the Chl and carotenoid transition dipole moments are identified. The obtained modeling parameters are used to simulate the CD spectra of two complexes with altered pigment composition: a mutant lacking Chls a 611-612 and a complex lacking the carotenoid neoxanthin. By removing the relevant pigment(s) from the structure, we are able to reproduce their spectra, which implies that the alteration does not disturb the overall structure. The CD spectrum of trimeric LHCII shows a reversed relative intensity of the two negative bands around 470 and 490 nm as compared to monomeric LHCII. The simulations reproduce this reversal, indicating that it is mainly due to interactions between chromophores in different monomeric subunits, and the trimerization does not induce observable changes in the monomeric structure. Our simulated spectrum resembles one of two different trimeric CD spectra reported in literature. We argue that the differences in the experimental trimeric CD spectra are caused by changes in the strength of the monomer-monomer interactions due to the differences in detergents used for the purification of the complexes.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Former Organization Units Biozentrum > Structural Biology (Aebi)
UniBasel Contributors:Georgakopoulou, Sofia
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:22 Mar 2012 14:19
Deposited On:22 Mar 2012 13:16

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