Wientjes E, Oostergetel GT, Jansson S, Boekema EJ. Croce R
The role of Lhca complexes in the supramolecular organization of higher plant photosystem I
Journal of Biological Chemistry: 2009 284(12):7800-7807

Abstract
In this work, Photosystem I supercomplexes have been purifiedfrom Lhca-deficient lines of Arabidopsis thaliana using a milddetergent treatment that does not induce loss of outer antennas.The complexes have been studied by integrating biochemical analysiswith electron microscopy. This allows the direct correlationof changes in protein content with changes in supramolecularstructure of Photosystem I to get information about the positionof the individual Lhca subunits, the association of the antennato the core, and the influence of the individual subunits onthe stability of the system. Photosystem I complexes with onlytwo or three antenna complexes were purified, showing that thebinding of Lhca1/4 and Lhca2/3 dimers to the core is not interdependent,although weak binding of Lhca2/3 to the core is stabilized bythe presence of Lhca4. Moreover, Lhca2 and Lhca4 can be associatedwith the core in the absence of their "dimeric partners." Thestructure of Photosystem I is very rigid, and the absence ofone antenna complex leaves a "hole" in the structure that cannotbe filled by other Lhcas, clearly indicating that the dockingsites for the individual subunits are highly specific. Thereis, however, an exception to the rule: Lhca5 can substitutefor Lhca4, yielding highly stable PSI supercomplexes with asupramolecular organization identical to the WT.

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