Orientation and linear dichroism of Mastigocladus laminosus phycocyanin trimer and Nostoc sp. phycocyanin dodecamer in stretched poly(vinyl alcohol) films

Laura J. Juszczak, Barbara A. Zilinskas, Nicholas Geacintov, Jacques Breton, Kenneth Sauer

Research output: Contribution to journalArticle

Abstract

The linear dichroism (LD) spectra of the C-phycocyanin (C-PC) trimer disks oriented in poly(vinyl alcohol) films (PVA) at room temperature and at 95 K were determined. Utilizing the known atomic coordinates of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677-695) and theoretical estimates of the orientations of the transition dipole moments relative to the molecular framework, the LD spectra were simulated using the pairwise exciton interaction model of Sauer and Scheer (Biochim. Biophys. Acta 936 (1988) 157-170); in this model, the α84 and β84 transition moments are coupled by an exciton mechanism, while the β155 chromophore remains uncoupled. Linear dichroism spectra calculated using this exciton model, as well as an uncoupled chromophore (molecular) model, were compared with experimental LD spectra. Satisfactory qualitative agreement can be obtained in both the exciton and molecular models using somewhat different relative values of the theoretically estimated magnitudes of the β155 oscillator strength. Because the relative contributions of each of the chromophores (and thus exciton components) to the overall absorption of the C-PC trimer are not known exactly, it is difficult to differentiate successfully between the molecular and exciton models at this time. The linear dichroism spectra of PC dodecamers derived from phycobilisomes of Nostoc sp. oriented in stretched PVA films closely resemble those of the C-PC trimers from Mastigocladus laminosus, suggesting that the phycocyanin chromophores are oriented in a similar manner in both cases, and that neither linker polypeptides nor the state of aggregation have a significant influence on these orientations and linear dichroism spectra. The LD spectra of oriented phycocyanins in stretched PVA films at low temperatures (95 K) appear to be of similar quality and magnitude as the LD spectra of single C-PC crystals (Schirmer, T. and Vincent, M.G. (1987) Biochim. Biophys. Acta 893, 379-385).

Original languageEnglish (US)
Pages (from-to)363-373
Number of pages11
JournalBBA - Bioenergetics
Volume1058
Issue number3
DOIs
StatePublished - Jul 5 1991

Fingerprint

Nostoc
Phycocyanin
Chromophores
Alcohols
Molecular Models
Dichroism
Phycobilisomes
Temperature
Dipole moment
LDS 751
Agglomeration
Peptides
Crystals

Keywords

  • Exciton model
  • Linear dichroism
  • Phycocyanin

ASJC Scopus subject areas

  • Biophysics

Cite this

Orientation and linear dichroism of Mastigocladus laminosus phycocyanin trimer and Nostoc sp. phycocyanin dodecamer in stretched poly(vinyl alcohol) films. / Juszczak, Laura J.; Zilinskas, Barbara A.; Geacintov, Nicholas; Breton, Jacques; Sauer, Kenneth.

In: BBA - Bioenergetics, Vol. 1058, No. 3, 05.07.1991, p. 363-373.

Research output: Contribution to journalArticle

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abstract = "The linear dichroism (LD) spectra of the C-phycocyanin (C-PC) trimer disks oriented in poly(vinyl alcohol) films (PVA) at room temperature and at 95 K were determined. Utilizing the known atomic coordinates of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677-695) and theoretical estimates of the orientations of the transition dipole moments relative to the molecular framework, the LD spectra were simulated using the pairwise exciton interaction model of Sauer and Scheer (Biochim. Biophys. Acta 936 (1988) 157-170); in this model, the α84 and β84 transition moments are coupled by an exciton mechanism, while the β155 chromophore remains uncoupled. Linear dichroism spectra calculated using this exciton model, as well as an uncoupled chromophore (molecular) model, were compared with experimental LD spectra. Satisfactory qualitative agreement can be obtained in both the exciton and molecular models using somewhat different relative values of the theoretically estimated magnitudes of the β155 oscillator strength. Because the relative contributions of each of the chromophores (and thus exciton components) to the overall absorption of the C-PC trimer are not known exactly, it is difficult to differentiate successfully between the molecular and exciton models at this time. The linear dichroism spectra of PC dodecamers derived from phycobilisomes of Nostoc sp. oriented in stretched PVA films closely resemble those of the C-PC trimers from Mastigocladus laminosus, suggesting that the phycocyanin chromophores are oriented in a similar manner in both cases, and that neither linker polypeptides nor the state of aggregation have a significant influence on these orientations and linear dichroism spectra. The LD spectra of oriented phycocyanins in stretched PVA films at low temperatures (95 K) appear to be of similar quality and magnitude as the LD spectra of single C-PC crystals (Schirmer, T. and Vincent, M.G. (1987) Biochim. Biophys. Acta 893, 379-385).",
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AU - Breton, Jacques

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