Characterization of expressed pigmented core light harvesting complex (LH 1) in a reaction center deficient mutant of Blastochloris viridis |
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Authors: | Ostafin Agnes E. Ponomarenko Nina S. Popova Julia A. Jäger Martin Bylina Edward J. Norris James R. |
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Affiliation: | (1) Present address: Department of Chemical Engineering, University of Notre Dame, 182 Fitzpatrick, Notre Dame, IN 46556, USA;(2) Department of Chemistry, Institute for Biophysical Dynamics, University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, USA;(3) KAIROS Scientific, 10225 Barnes Canyon Road #A110, San Diego, CA 92121, USA |
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Abstract: | The utility of photosynthetically defective mutants in the purple photosynthetic bacterium Blastochloris viridis (formerly Rhodopseudomonas viridis)was demonstrated with construction of a reaction-center deficient mutant, LH 1-H. This LH 1-H mutant has a photosynthetic apparatus in which most of the puf operon genes were deleted, resulting in an organism containing only the genes for the light harvesting polypeptides and the H subunit of the reaction center. This B. viridisstrain containing a truncation of the puf operon was characterized by gel electrophoresis, lipid-to-protein ratio analysis, optical spectroscopy, electron paramagnetic resonance and transmission electron microscopy. Optical and electron paramagnetic resonance spectroscopies revealed no photoactivity in this LH 1-H mutant consistent with the absence of intact reaction centers. Electron paramagnetic resonance evidence for assembled LH 1 complexes suggested that the interactions between light harvesting polypeptide complexes in membranes were largely unchanged despite the absence of their companion reaction center cores. The observed increase in the lipid-to-protein ratio was consistent with modified interactions between LH 1s, a view supported by transmission electron microscopy analysis of membrane fragments. The results show that B. viridis can serve as a practical system for investigating structure-function relationships in membranes and photosynthesis through the construction of photosynthetically defective mutants. This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | Blastochloris viridis (formerly Rhodopseudomonas viridis) EPR LH 1 mutant TEM |
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