title: Structural variability in wild-type and bchQ bchR mutant chlorosomes of the green sulfur bacterium Chlorobaculum tepidum.
abstract: The self-aggregated state of bacteriochlorophyll (BChl) c molecules in chlorosomes belonging to a bchQ bchR mutant of the green sulfur bacteria Chlorobaculum tepidum, which mostly produces a single 17(2)-farnesyl-(R)-[8-ethyl,12-methyl]BChl c homologue, was characterized by solid-state nuclear magnetic resonance (NMR) spectroscopy and high-resolution electron microscopy. A nearly complete (1)H and (13)C chemical shift assignment was obtained from well-resolved homonuclear (13)C-(13)C and heteronuclear (1)H-(13)C NMR data sets collected from (13)C-enriched chlorosome preparations. Pronounced doubling (1:1) of specific (13)C and (1)H resonances revealed the presence of two distinct and nonequivalent BChl c components, attributed to all syn- and all anti-coordinated parallel stacks, depending on the rotation of the macrocycle with respect to the 3(1)-methyl group. Steric hindrance from the 20-methyl functionality induces structural differences between the syn and anti forms. A weak but significant and reproducible reflection at 1/0.69 nm(-1) in the direction perpendicular to the curvature of cylindrical segments observed with electron microscopy also suggests parallel stacking of BChl c molecules, though the observed lamellar spacing of 2.4 nm suggests weaker packing than for wild-type chlorosomes. We propose that relaxation of the pseudosymmetry observed for the wild type and a related BChl d mutant leads to extended domains of alternating syn and anti stacks in the bchQ bchR chlorosomes. Domains can be joined to form cylinders by helical syn-anti transition trajectories. The phase separation in domains on the cylindrical surface represents a basic mechanism for establishing suprastructural heterogeneity in an otherwise uniform supramolecular scaffolding framework that is well-ordered at the molecular level.
authors.affiliation: Leiden Institute of Chemistry, Leiden University, 2300 RA Leiden, The Netherlands.
authors.forename: Swapna
authors.initials: S
authors.lastname: Ganapathy
authors.forename: Gert T
authors.initials: GT
authors.lastname: Oostergetel
authors.forename: Michael
authors.initials: M
authors.lastname: Reus
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsukatani
authors.forename: Aline
authors.initials: A
authors.lastname: Gomez Maqueo Chew
authors.forename: Francesco
authors.initials: F
authors.lastname: Buda
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
authors.forename: Alfred R
authors.initials: AR
authors.lastname: Holzwarth
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: de Groot
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000235:genetics; D019414:Chlorobi / Q000737:chemistry* / Q000235:genetics* / Q000648:ultrastructure; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; C002084:bacteriochlorophyll c