Membrane curvature induced by aggregates of LH2s and monomeric LH1s.
The photosynthetic apparatus of purple bacteria is contained within organelles called chromatophores, which form as extensions of the cytoplasmic membrane. The shape of these chromatophores can be spherical (as in Rhodobacter sphaeroides), lamellar (as in Rhodopseudomonas acidophila and Phaeospirillum molischianum), or tubular (as in certain Rb. sphaeroides mutants). Chromatophore shape is thought to be influenced by the integral membrane proteins Light Harvesting Complexes I and II (LH1 and LH2), which pack tightly together in the chromatophore. It has been suggested that the shape of LH2, together with its close packing in the membrane, induces membrane curvature. The mechanism of LH2-induced curvature is explored via molecular dynamics simulations of multiple LH2 complexes in a membrane patch. LH2s from three species-Rb. sphaeroides, Rps. acidophila, and Phsp. molischianum-were simulated in different packing arrangements. In each case, the LH2s pack together and tilt with respect to neighboring LH2s in a way that produces an overall curvature. This curvature appears to be driven by a combination of LH2's shape and electrostatic forces that are modulated by the presence of well-conserved cytoplasmic charged residues, the removal of which inhibits LH2 curvature. The interaction of LH2s and an LH1 monomer is also explored, and it suggests that curvature is diminished by the presence of LH1 monomers. The implications of our results for chromatophore shape are discussed.
Chandler
Danielle E
DE
Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Gumbart
James
J
Stack
John D
JD
Chipot
Christophe
C
Schulten
Klaus
K
D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D050356:Lipid Metabolism; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D055672:Static Electricity
D045342:Light-Harvesting Protein Complexes