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

Robert MacColl, Henryk Malak, Ignacy Gryczynski, Leslie E. Eisele, G. J. Mizejewski, Ercole Franklin, Hesham Sheikh, Daniel Montellese, Scott Hopkins, Laurie C. MacColl

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21 Scopus citations

Abstract

Phycoerythrin 545 was isolated having an α2β2 (dimer) protein structure at pH 6.0 and 2 g/L protein concentration with eight bilin chromophores. Monomers (αβ) 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 α2β2 dimers, although they have very similar protein secondary structures. The optical spectra of phycoerythrin 545 showed four types of behavior with temperature: 10-20 °C, dimers; 40-50 °C, dimers/monomers; 60 °C, nearly fully disordered; 70 °C, disordered α and β polypeptides. At 40 °C, the protein dissociated partially to monomer, which could be totally reversed to dimers at 20-25 °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 showed the fastest time for protein dimers to be 2.4 ps and monomers had a 39-ps lifetime. Phycocyanin 645 was found to have a 550-fs lifetime.

Original languageEnglish
Pages (from-to)417-423
Number of pages7
JournalBiochemistry
Volume37
Issue number1
DOIs
StatePublished - 6 Jan 1998

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