PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

X-ray structure of the pea light harvesting complex II at 2.5 A resolution. Joerg Standfuss^*,1, Anke Terwisscha von Scheltinga¹, Heidi Betz¹, Werner Kühlbrandt¹, ¹ Max-Planck-Institute of biophysics, Frankfurt/M, Germany

ABSTRACT- The light harvesting complex II (LHC-II) is the major collector of solar energy in all green plants and binds about half of their total Chlorophyll. LHC-II is a trimer in the photosynthetic membrane of nearly identical monomers. Each monomer binds a number of chlorophyll and carotenoid molecules accounting for about 30% of the total pigment/protein complexes molecular mass. In addition to the light harvesting, LHC-II is involved in several photoprotective and regulative processes in plant photosynthesis. LHC-II purified from pea leaves and recombinant refolded LHC-II were crystallized by vapor diffusion. Crystals showed diffraction up to 2.2 A and data with an effective resolution of 2.5 A have been collected. The 3D crystals consist of stacks of 2D crystals (type I membrane protein crystals) and show, in contrast to the type III crystals used for the recent spinach LHC-II structure, no contacts mediated by the lipid DGDG. Molecular replacement with experimental EM electron density was used for phasing and resulted after density averaging in a high quality electron density map. Using this map and the 3.4 A pea LHC-II structure as a starting point most of the pigment/protein complex could be positioned. This resulted in a well-refined X-ray structure with a R-factor of 23.6% and a R-free of 25.6%, respectively.

KEY WORDS: pea, light harvesting complex, structure