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Reaction centers from three herbicide-resistant mutants of Rhodobacter sphaeroides 2.4.1: sequence analysis and
M L Paddock1, S H Rongey, E C Abresch
1Department of Physics-B-019, University of California, San Diego at La Jolla, 92093, CA, USA.
Photosynthesis Research
|January 17, 2014
Summary
Photosynthetic bacteria mutants resistant to herbicides like terbutryne were identified. These mutations in the L-subunit alter the quinone binding site, explaining herbicide inhibition and revealing functional similarities with plant photosystem II.
Area of Science:
- Biochemistry
- Molecular Biology
- Photosynthesis Research
Background:
- Herbicides inhibiting plant photosynthesis often affect bacterial photosynthesis.
- Photosynthetic bacteria like Rhodobacter sphaeroides offer a model for studying these processes.
Purpose of the Study:
- To isolate and characterize mutants of Rhodobacter sphaeroides resistant to the herbicide terbutryne.
- To elucidate the molecular mechanisms of herbicide resistance and inhibition in bacterial photosynthesis.
Main Methods:
- Isolation of herbicide-resistant mutants.
- Recombinant DNA techniques for primary structure determination.
- Biochemical characterization of reaction centers (electron transfer rates, inhibition constants).
- X-ray crystallography analysis for structural insights.
Main Results:
- Three terbutryne-resistant mutants were identified, also showing resistance to o-phenanthroline.
- Mutations were located on the L-subunit, altering amino acids Ile(229) → Met, Ser(223) → Pro, and Tyr(222) → Gly.
- These altered amino acids are part of the secondary quinone (Q b) binding pocket, consistent with competitive herbicide inhibition.
- Functional analogy between the bacterial L-subunit and plant D1 subunit was strengthened by a mutation analogous to Ser(264) in photosystem II.
Conclusions:
- Herbicides like terbutryne and o-phenanthroline competitively inhibit electron transfer by binding to the Q b site.
- The L-subunit of Rhodobacter sphaeroides plays a crucial role in herbicide binding and photosynthetic electron transport.
- Structural and functional similarities exist between bacterial and plant photosynthetic systems.
