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BY-NC-ND 3.0 license Open Access Published by De Gruyter June 2, 2014

Circular Dichroism of C-Phycoerythrin: A Conformational Analysis

Elisabeth Langer, Harald Lehner, Wolfhart Rüdiger and Barbara Zickendraht-Wendelstadt

Abstract

An extensive study of the chiroptical properties of C-phycoerythrin and the α-and β-subunits in the spectral region from 700 -200 nm is presented.

Based on the VIS-circular dichroism inherently chiral conform ations are proposed for the co­ valently linked chromophores.

By means of mean residue ellipticities and the experimental circular dichroism spectra in the region of the n → π* peptide transition the a-helix contents of the apoproteins of the ac-and ß-subunits are estimated to amount to 60% and 40%, respectively. The circular dichroism spectrum of native C-phycoerythrin is congruent with a linear superposition of the α-and β-subspectra, in the whole spectral region studied. Since a-and β-subunits are associated in native C-phycoery-thrin as revealed by sedim entation analysis the interactions between the subunits in the native chromoprotein are not accom panied by substantial conform ational changes. In the temperature range 0°-40°C the thermally induced changes of the chrom ophores in native C-phycoerythrin are not associated with changes of the secondary structure of the apoprotein. Unfolding occurs at 60°-70°C but slowly leads to irreversible denaturation.

Protein unfolding starts at 3 M urea. The random coil secondary structure of the apoproteins is reached at 8 M urea. At this concentration the absorbance and the optical activity of the chrom o­ phores are reduced by a factor 3 and 10, respectively. The conformational changes in the peptide with increasing denaturant concentration are not synchronous with those induced in the Chromo­ phore indicating that a m ultistep process is operative during unfolding. The C D results on dena­ turation are supplem ented by absorption and em ission spectroscopy.

Received: 1980-2-5
Published Online: 2014-6-2
Published in Print: 1980-6-1

© 1946 – 2014: Verlag der Zeitschrift für Naturforschung

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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