Intrinsic curvature properties of photosynthetic proteins in chromatophores.
In purple bacteria, photosynthesis is carried out on large indentations of the bacterial plasma membrane termed chromatophores. Acting as primitive organelles, chromatophores are densely packed with the membrane proteins necessary for photosynthesis, including light harvesting complexes LH1 and LH2, reaction center (RC), and cytochrome bc(1). The shape of chromatophores is primarily dependent on species, and is typically spherical or flat. How these shapes arise from the protein-protein and protein-membrane interactions is still unknown. Now, using molecular dynamics simulations, we have observed the dynamic curvature of membranes caused by proteins in the chromatophore. A membrane-embedded array of LH2s was found to relax to a curved state, both for LH2 from Rps. acidophila and a homology-modeled LH2 from Rb. sphaeroides. A modeled LH1-RC-PufX dimer was found to develop a bend at the dimerizing interface resulting in a curved shape as well. In contrast, the bc(1) complex, which has not been imaged yet in native chromatophores, did not induce a preferred membrane curvature in simulation. Based on these results, a model for how the different photosynthetic proteins influence chromatophore shape is presented.
Department of Physics, University of Illinois at Urbana-Champaign, USA.
Danielle E
DE
Chandler
Jen
J
Hsin
Christopher B
CB
Harrison
James
J
Gumbart
Klaus
K
Schulten
D000595:Amino Acid Sequence; D020130:Bacterial Chromatophores / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D014450:Electron Transport Complex III / Q000737:chemistry / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010788:Photosynthesis; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012241:Rhodopseudomonas / Q000378:metabolism*
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D014450:Electron Transport Complex III