The Journal of Cell Biology, Vol 100, 552-557, Copyright © 1985 by The Rockefeller University Press
Reconstitution of light-harvesting complexes and photosystem II cores into galactolipid and phospholipid liposomes
SG Sprague, EL Camm, BR Green and LA Staehelin
Chlorophyll a/b light-harvesting complexes (chl a/b LHC) and photosystem II
(PSII) cores were isolated from an octyl glucoside- containing sucrose
gradient after solubilization of barley thylakoid membranes with Triton
X-100 and octyl glucoside. No cation precipitation step was necessary to
collect the chl a/b LHC. PAGE under mildly denaturing and fully denaturing
conditions showed that the chl a/b LHC fraction contained
chlorophyll-protein complexes CP27, CP29, and CP64. The PSII core material
contained CP43 and CP47, and little contamination by other nonpigmented
polypeptides. Freeze-fracture electron microscopy of the chl a/b LHC after
reconstitution into digalactosyldiglyceride (DG) or phosphatidylcholine
(PC) vesicles showed that the protein particles (approximately 7.5 +/- 1.6
nm) were approximately 99 and 90% randomly dispersed, respectively, in the
liposomes. Addition of Mg++ produced particle aggregation and membrane
adhesion in chl a/b LHC-DG liposomes in a manner analogous to that
described for LHC-PC liposomes. Reconstitution of PSII cores into DG
vesicles also produced proteoliposomes with randomly dispersed particles
(approximately 7.5 +/- 1.6 nm). In contrast, PSII-PC mixtures formed
convoluted networks of tubular membranes that exhibited very few fracture
faces. Most of the protein particles (approximately 7.0 +/- 1.5 nm) were
seen trapped between, rather than embedded in, the membranes. The
interaction between the zwitterionic head group of the phosphatidyl choline
and the negatively charged PSII core may be responsible for the unusual
membrane structures observed.
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