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Related Experiment Videos

R-phycoerythrins having two conformations for the same aggregate.

R MacColl1, L E Eisele

  • 1New York State Department of Health, Wadsworth Center, P.O. Box 509, Albany, NY 12201-0509, USA. robert.maccoll@wadsworth.org

Biophysical Chemistry
|October 30, 1996
PubMed
Summary
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R-phycoerythrin proteins can exist in two distinct conformations, differing in tertiary structure but not secondary structure. These conformational changes influence chromophore properties, as observed through circular dichroism (CD) spectroscopy.

Area of Science:

  • Biochemistry
  • Spectroscopy
  • Structural Biology

Background:

  • R-phycoerythrin, a biliprotein, plays a crucial role in light harvesting for photosynthesis in red algae and cyanobacteria.
  • Circular dichroism (CD) spectroscopy is a powerful tool for probing the structure and conformational changes of proteins and their chromophores.

Purpose of the Study:

  • To investigate the conformational flexibility of R-phycoerythrin from Porphyra tenera and Gastroclonium coulteri.
  • To characterize subtle structural changes affecting chromophores using visible CD spectroscopy.
  • To determine if R-phycoerythrin aggregates can adopt multiple conformations.

Main Methods:

  • Visible and far-UV CD spectroscopy to analyze protein structure and chromophore environment.
  • Treatment with denaturants (urea, sodium thiocyanate) to induce spectral changes.

Related Experiment Videos

  • Fluorescence spectroscopy to assess energy migration.
  • Deconvolution of CD spectra for chromophore analysis.

    • Main Results:

    • R-phycoerythrin (Porphyra tenera) exhibited slow spectral changes in aqueous buffer, with a red shift and intensity increase of a band at 489 nm.
    • Urea and sodium thiocyanate accelerated these spectral changes without altering visible absorption or far-UV CD spectra.
    • A second R-phycoerythrin (Gastroclonium coulteri) showed a novel negative CD band, which converted to a positive band upon urea treatment.
    • Fluorescence studies confirmed that urea treatment did not affect energy migration.
    • Deconvolution revealed that the same R-phycoerythrin aggregates could exist in two distinct conformations.

    Conclusions:

    • R-phycoerythrin aggregates can adopt at least two different tertiary structures while maintaining their secondary structure.
    • These conformational changes, though subtle, significantly impact the visible CD spectra of the chromophores.
    • This finding represents a novel observation for red algal and cyanobacterial biliproteins, highlighting their structural adaptability.