A quantum mechanical analysis of the light-harvesting complex 2 (LH2) from purple photosynthetic bacteria: insights into the electrostatic effects of transmembrane helices.
We perform a quantum mechanical study of the peptides that are part of the LH2 complex from Rhodopseudomonas acidophila, a non-sulfur purple bacteria that has the ability of producing chemical energy from photosynthesis. The electronic structure calculations indicate that the transmembrane helices of these peptides are characterized by dipole moments with a magnitude of about 150D. When the full nonamer assembly made of 18 peptides is considered, then a macrodipole of magnitude 806D is built up from the vector sum of each monomer dipole. The macrodipole is oriented normal to the membrane plane and with the positive tip toward the cytoplasm thereby indicating that the electronic charge of the protein scaffold is polarized toward the periplasm. The results obtained here suggest that the asymmetric charge distribution of the protein scaffold contributes an anisotropic electrostatic environment which differentiates the absorption properties of the bacteriochlorophyll pigments, B800 and B850, embedded in the LH2 complex.
Pichierri
Fabio
F
G-COE Laboratory, Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. fabio@che.tohoku.ac.jp
D001426:Bacterial Proteins / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D008958:Models, Molecular; D015394:Molecular Structure; D010788:Photosynthesis / Q000502:physiology*; D011789:Quantum Theory; D012241:Rhodopseudomonas; D055672:Static Electricity
C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes