Phycoerythrin 545: monomers, energy migration, bilin topography, and monomer/dimer equilibrium

Biochemistry
R MacCollL C MacColl

Abstract

Phycoerythrin 545 was isolated having an alpha2beta2 (dimer) protein structure at pH 6.0 and 2 g/L protein concentration with eight bilin chromophores. Monomers (alphabeta) were produced by lowering the protein concentration to 0.15 g/L and the pH to 4.5. Dimer dissociation was monitored by dynamic light scattering and gel-filtration column chromatography. Monomers were stable and had bilin optical spectra different from the alpha2beta2 dimers, although they have very similar protein secondary structures. The optical spectra of phycoerythrin 545 showed four types of behavior with temperature: 10-20 degrees C, dimers; 40-50 degrees C, dimers/monomers; 60 degrees C, nearly fully disordered; 70 degrees C, disordered alpha and beta polypeptides. At 40 degrees C, the protein dissociated partially to monomer, which could be totally reversed to dimers at 20-25 degrees C. The visible circular dichroism difference spectrum for the protein dimers minus monomers exhibited positive and negative bands--such spectra may indicate exciton splitting between closely-spaced bilins. Circular dichroism also revealed a spectrum suggesting exciton coupling for the second excited state of the bilins. Ultrafast fluorescence using a two-photon method sh...Continue Reading

Citations

Oct 19, 2004·Journal of Photochemistry and Photobiology. B, Biology·Li SunLixue Chen
Oct 18, 2001·Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy·J HofkensF C De Schryver
Sep 13, 2003·Advances in Colloid and Interface Science·Vladimir M Gun'koRoman Leboda
Sep 14, 1999·Biochimica Et Biophysica Acta·R MacCollJ Marrone
Feb 21, 2004·Photochemistry and Photobiology·Danuta FrackowiakBogumil Zelent
Mar 2, 1999·Journal of Structural Biology·R MacColl

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