Structural variability in wild-type and bchQ bchR mutant chlorosomes of the green sulfur bacterium Chlorobaculum tepidum

Swapna Ganapathy, Gert T. Oostergetel, Michael Reus, Yusuke Tsukatani, Aline Gomez Maqueo Chew, Francesco Buda, Donald A. Bryant, Alfred R. Holzwarth, Huub J.M. De Groot

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38 Scopus citations

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 172-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 1H and 13C chemical shift assignment was obtained from well-resolved homonuclear 13C- 13C and heteronuclear 1H-13C NMR data sets collected from 13C-enriched chlorosome preparations. Pronounced doubling (1:1) of specific 13C and 1H 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 31-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. (Figure Presented).

Original languageEnglish (US)
Pages (from-to)4488-4498
Number of pages11
JournalBiochemistry
Volume51
Issue number22
DOIs
StatePublished - Jun 5 2012

All Science Journal Classification (ASJC) codes

  • Biochemistry

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