The light-harvesting chlorophyll a/b complex (LHC-II) found in green plants has at least three functions: it absorbs light energy for transfer to the reaction centers, it is involved in keeping the photosynthetic membranes stacked, and it regulates energy distribution between the two photosystems. We have developed a procedure to produce large vesicles consisting almost exclusively of two-dimensional crystalline domains of LHC-II in which LHC-II is biochemically and structurally intact, as shown by SDS-PAGE, response to cations, and 77K fluorescence excitation spectra. The vesicles were examined by cryoelectron microscopy and analyzed, in projection, to a resolution of 17 A. Their surface lattice consists of trimers arranged in interlocking circles; the two-sided plane group is p321 (unit cell dimension, a = 124 A) with two, oppositely facing trimers/unit cell. Individual trimers consist of matter arranged in a ring, around a central cavity, an appearance similar to that obtained in some conditions using negative stain (Li, J., 1985. Proc. Natl. Acad. Sci. USA. 82:386-390). The monomer (approximately 45 x 20 A) is seen as two domains of slightly different size at this resolution. The thickness of single layers is approximately 48 A, measured from edge-on views of the frozen vesicles. Based on these dimensions, the molecular mass of the monomer is approximately 30 kD. Therefore, each monomer appears to be composed of a single polypeptide and its associated pigments.
Article|
May 01 1988
Two-dimensional structure of the light-harvesting chlorophyll a/b complex by cryoelectron microscopy.
M K Lyon
Department of Cell Biology, Stanford University School of Medicine, California 94305.
P N Unwin
Department of Cell Biology, Stanford University School of Medicine, California 94305.
Online ISSN: 1540-8140
Print ISSN: 0021-9525
J Cell Biol (1988) 106 (5): 1515–1523.
Citation
M K Lyon, P N Unwin; Two-dimensional structure of the light-harvesting chlorophyll a/b complex by cryoelectron microscopy.. J Cell Biol 1 May 1988; 106 (5): 1515–1523. doi: https://doi.org/10.1083/jcb.106.5.1515
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