Characterization of a highly purified, fully active, crystallizable RC-LH1-PufX core complex from Rhodobacter sphaeroides.
Photosynthetic complexes in bacteria absorb light and undergo photochemistry with high quantum efficiency. We describe the isolation of a highly purified, active, reaction center-light-harvesting 1-PufX complex (RC-LH1-PufX core complex) from a strain of the photosynthetic bacterium, Rhodobacter sphaeroides, which lacks the light-harvesting 2 (LH2) and contains a 6 histidine tag on the H subunit of the RC. The complex was solubilized with diheptanoyl-sn-glycero-3-phosphocholine (DHPC), and purified by Ni-affinity, size-exclusion and ion-exchange chromatography in dodecyl maltoside. SDS-PAGE analysis shows the complex to be highly purified. The quantum efficiency was determined by measuring the charge separation (DQA --> D+QA -) in the RC as a function of light intensity. The RC-LH1-PufX complex had a quantum efficiency of 0.95 +/- 0.05, indicating full activity. The stoichiometry of LH1 subunits per RC was determined by two independent methods: (i) solvent extraction and absorbance spectroscopy of bacteriochlorophyll, and (ii) density scanning of the SDS-PAGE bands. The average stoichiometry from the two measurements was 13.3 +/- 0.9 LH1/RC. The presence of PufX was observed in SDS-PAGE gels at a stoichiometry of 1.1 +/- 0.1/RC. Crystals of the core complex have been obtained which diffract X-rays to 12 A. A preliminary analysis of the space group and unit cell analysis indicated a P1 space group with unit cell dimensions of a = 76.3 A, b = 137.2 A, c = 137.5 A; alpha = 60.0 degrees , beta = 89.95 degrees , gamma =90.02 degrees .
Abresch
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Department of Physics, University California San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
Axelrod
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Beatty
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JT
Johnson
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Nechushtai
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Paddock
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D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D003460:Crystallization; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; C088749:PufX protein, Rhodobacter