Structure of chlorosomes from the green filamentous bacterium Chloroflexus aurantiacus.
The green filamentous bacterium Chloroflexus aurantiacus employs chlorosomes as photosynthetic antennae. Chlorosomes contain bacteriochlorophyll aggregates and are attached to the inner side of a plasma membrane via a protein baseplate. The structure of chlorosomes from C. aurantiacus was investigated by using a combination of cryo-electron microscopy and X-ray diffraction and compared with that of Chlorobi species. Cryo-electron tomography revealed thin chlorosomes for which a distinct crystalline baseplate lattice was visualized in high-resolution projections. The baseplate is present only on one side of the chlorosome, and the lattice dimensions suggest that a dimer of the CsmA protein is the building block. The bacteriochlorophyll aggregates inside the chlorosome are arranged in lamellae, but the spacing is much greater than that in Chlorobi species. A comparison of chlorosomes from different species suggested that the lamellar spacing is proportional to the chain length of the esterifying alcohols. C. aurantiacus chlorosomes accumulate larger quantities of carotenoids under high-light conditions, presumably to provide photoprotection. The wider lamellae allow accommodation of the additional carotenoids and lead to increased disorder within the lamellae.
Psencík
Jakub
J
Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
Collins
Aaron M
AM
Liljeroos
Lassi
L
Torkkeli
Mika
M
Laurinmäki
Pasi
P
Ansink
Hermanus M
HM
Ikonen
Teemu P
TP
Serimaa
Ritva E
RE
Blankenship
Robert E
RE
Tuma
Roman
R
Butcher
Sarah J
SJ
D020130:Bacterial Chromatophores; D001429:Bacteriochlorophylls / Q000502:physiology; D002462:Cell Membrane; D041861:Chloroflexus / Q000378:metabolism*; D007425:Intracellular Membranes; D045342:Light-Harvesting Protein Complexes / Q000502:physiology*; D015388:Organelles / Q000502:physiology* / Q000648:ultrastructure; D014961:X-Ray Diffraction
D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes