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Related Experiment Videos

Aspartic acid substitutions affect proton translocation by bacteriorhodopsin.

T Mogi1, L J Stern, T Marti

  • 1Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.

Proceedings of the National Academy of Sciences of the United States of America
|June 1, 1988
PubMed
Summary

Investigating bacteriorhodopsin proton translocation, researchers substituted aspartic acid residues. Key mutations, particularly Asp-85, significantly impaired proton pumping, revealing critical roles for specific aspartic acids in this essential biological process.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • Bacteriorhodopsin is a light-driven proton pump crucial for cellular energy generation.
  • Understanding the mechanism of proton translocation is vital for deciphering energy transduction in biological systems.

Purpose of the Study:

  • To elucidate the role of individual aspartic acid residues in bacteriorhodopsin's proton translocation pathway.
  • To investigate the functional impact of specific amino acid substitutions on proton pumping efficiency.

Main Methods:

  • Site-directed mutagenesis was used to replace aspartic acid residues with asparagine, glutamic acid, or alanine.
  • Mutant bacteriorhodopsin genes were expressed in Escherichia coli, and proteins were purified.
  • Proton pumping activity and chromophore regeneration rates of mutants were analyzed.

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Main Results:

  • All purified mutant proteins regenerated bacteriorhodopsin-like chromophores, though with varying rates and spectral properties.
  • The Asp-85 to asparagine mutant exhibited no detectable proton pumping activity.
  • Mutants Asp-96 to asparagine and Asp-212 to glutamic acid showed <10% proton pumping, while Asp-115 to glutamic acid showed ~30% activity.

Conclusions:

  • Specific aspartic acid residues, particularly Asp-85, are essential for efficient proton translocation in bacteriorhodopsin.
  • The findings challenge the external point charge model for opsin shifts.
  • This study provides critical insights into the molecular mechanism of proton pumping by bacteriorhodopsin.