title: Assembly of a mixture of isomeric BChl c from Chlorobium limicola as determined by intermolecular 13C-13C dipolar correlations: coexistence of dimer-based and pseudo-monomer-based stackings.
abstract: A mixture of bacteriochlorophyll (BChl) c isomers was extracted from the cells of Chlorobium limicola that were grown in the media of 13C-enriched and natural-abundance isotopic compositions. The magic-angle spinning 13C NMR proton-driven spin-diffusion spectra were recorded with mixing times of 50, 100, and 250 ms for two different kinds of in vitro aggregates, one consisting of pure [13C]BChl c and the other consisting of a 1:1 mixture of [13C]BChl c and [12C]BChl c; those peaks whose intensities were reduced to approximately 1/4 by this dilution were assigned to intermolecular 13C-13C dipolar correlation peaks. On the other hand, the nearest-neighbor intermolecular carbon-carbon close contacts with distances of 4-6 A were simulated, to predict observed correlation peaks, for six different models of BChl c assembly. They include weakly overlapped monomers forming structure 1 and structure 2, strongly overlapped dimers forming straight and inclined columns, and weakly overlapped dimers forming aligned and displaced layers. Comparison between the observed correlation peaks and the predicted carbon-carbon close contacts, for both the macrocycles and the side chains, led us to a conclusion that the weakly overlapped dimers forming displaced layers are most likely the assembly of the BChl c molecules in the aggregate.
authors.affiliation: Faculty of Science and Technology, Kwansei Gakuin University, Gakuen, Sanda 669-1337, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kakitani
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Nagae
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Ayako
authors.initials: A
authors.lastname: Egawa
authors.forename: Kengo
authors.initials: K
authors.lastname: Akiba
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Hideo
authors.initials: H
authors.lastname: Akutsu
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Koyama
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002247:Carbon Isotopes; D041883:Chlorobium / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D066298:In Vitro Techniques; D007536:Isomerism; D008956:Models, Chemical; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D002247:Carbon Isotopes