title: Anisotropic circular dichroism signatures of oriented thylakoid membranes and lamellar aggregates of LHCII.
abstract: In photosynthesis research, circular dichroism (CD) spectroscopy is an indispensable tool to probe molecular architecture at virtually all levels of structural complexity. At the molecular level, the chirality of the molecule results in intrinsic CD; pigment-pigment interactions in protein complexes and small aggregates can give rise to excitonic CD bands, while "psi-type" CD signals originate from large, densely packed chiral aggregates. It has been well established that anisotropic CD (ACD), measured on samples with defined non-random orientation relative to the propagation of the measuring beam, carries specific information on the architecture of molecules or molecular macroassemblies. However, ACD is usually combined with linear dichroism and can be distorted by instrumental imperfections, which given the strong anisotropic nature of photosynthetic membranes and complexes, might be the reason why ACD is rarely studied in photosynthesis research. In this study, we present ACD spectra, corrected for linear dichroism, of isolated intact thylakoid membranes of granal chloroplasts, washed unstacked thylakoid membranes, photosystem II (PSII) membranes (BBY particles), grana patches, and tightly stacked lamellar macroaggregates of the main light-harvesting complex of PSII (LHCII). We show that the ACD spectra of face- and edge-aligned stacked thylakoid membranes and LHCII lamellae exhibit profound differences in their psi-type CD bands. Marked differences are also seen in the excitonic CD of BBY and washed thylakoid membranes. Magnetic CD (MCD) spectra on random and aligned samples, and the largely invariable nature of the MCD spectra, despite dramatic variations in the measured isotropic and anisotropic CD, testify that ACD can be measured without substantial distortions and thus employed to extract detailed information on the (supra)molecular organization of photosynthetic complexes. An example is provided showing the ability of CD data to indicate such an organization, leading to the discovery of a novel crystalline structure in macroaggregates of LHCII.
authors.affiliation: Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 521, 6701, Szeged, Hungary.
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Miloslavina
authors.forename: Petar H
authors.initials: PH
authors.lastname: Lambrev
authors.forename: Tamás
authors.initials: T
authors.lastname: Jávorfi
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Várkonyi
authors.forename: Václav
authors.initials: V
authors.lastname: Karlický
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Wall
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Hind
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
mesh_terms: D016880:Anisotropy; D002942:Circular Dichroism / Q000379:methods*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000302:isolation & purification / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000302:isolation & purification / Q000528:radiation effects; D018724:Spinacia oleracea / Q000737:chemistry* / Q000528:radiation effects; D020524:Thylakoids / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex