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FORMATION OF CRYSTALLINE ARRAYS OF CHLOROPHYLL a/b- LIGHT-HARVESTING PROTEIN BY MEMBRANE RECONSTITUTION
| Citations: | 3 - 0 self |
BibTeX
@MISC{Li_formationof,
author = {Jade Li and Carol Hollingshead},
title = {FORMATION OF CRYSTALLINE ARRAYS OF CHLOROPHYLL a/b- LIGHT-HARVESTING PROTEIN BY MEMBRANE RECONSTITUTION},
year = {}
}
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Abstract
ABSTRACT The structure of the major protein constituent of photosynthetic membranes in higher plants, the chlorophyll a/b-light harvesting complex (LHC), was studied by x-ray diffraction and electron microscopy. TheLHC was purified from Triton X-100 solubilized thylakoid membranes ofthe pea, and contained 6 mol of chlorophylls a and b per mole of a polypeptide of 27,000 molecular weight. X-ray diffraction showed that in the presence of 10 mM MgCl2, purified LHC forms planar aggregates that stack with a period of 51 A. Within each layer, LHC molecules pack with a center-to-center distance of 85 A but without long-range order. However, when LHC is incorporated into single-walled vesicles of plant lecithin, the addition ofNaCl above 10mM, or MgCl2 above 2 mM, led to the formation ofplaques of hexagonal lattices, with a lattice constant of 125 A. The large domain size and high degree oforder in the plane of the membrane are evident from the sharp lattice lines observed to 7 A resolution on the equator of the x-ray pattern. Freeze-fracture electron micrographs demonstrated an aligned stacking of the lattices in adjacent membranes, resulting in crystallinity in the third dimension over short distances. Micrographs of negatively stained membranes revealed a hexagonal lattice of the same lattice constant, formed by surface-exposed parts oftheLHC molecules which are probably responsible for the ordered stacking of lattices. In both the LHC aggregates and in the reconstituted membrane lattices the diffracted x-ray intensities at 10-A spacing on the equator indicate that the LHC molecule contains paralled a-helices or f-sheets that are oriented perpendicular to the planar arrays.
Keyphrases
light-harvesting protein membrane reconstitution formation crystalline array chlorophyll hexagonal lattice x-ray diffraction lattice constant third dimension sharp lattice line single-walled vesicle addition ofnacl lhc molecule contains molecular weight diffracted x-ray intensity adjacent membrane formation ofplaques thylakoid membrane reconstituted membrane short distance photosynthetic membrane high degree oforder lhc form electron microscopy triton x-100 freeze-fracture electron micrographs long-range order center-to-center distance ordered stacking lhc aggregate large domain size planar array plant lecithin mm mgcl2 surface-exposed part b-light harvesting complex aligned stacking major protein constituent x-ray pattern
