The free energy of dissociation of oligomeric structure in phycocyanin is not linear with denaturant

Katie L. Thoren, Katelyn B. Connell, Taylor E. Robinson, David D. Shellhamer, Margaret S. Tammaro, Yvonne M. Gindt

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

Using SEC HPLC and fluorescence anisotropy, absorption spectra were assigned to the specific oligomeric structures found with phycocyanin. The absorption spectra were used to quantify the population of each oligomeric form of the protein as a function of both urea concentration and temperature. Phycocyanin hexamers dissociate to trimers with equilibrium constants of 10 -6 to 10-5. Phycocyanin trimers dissociate to monomers with equilibrium constants of 10-15 to 10-12. Both dissociation constants increase linearly with increasing urea concentration, and ΔG° values calculated from the equilibrium constants fit best with an exponential function. Our findings appear in contrast with the commonly used linear extrapolation model, ΔGurea° = ΔG water° + A[denaturant], in which a linear relationship exists between the free energy of protein unfolding or loss of quaternary structure and the denaturant concentration. Our data examines a smaller range of denaturant concentration than generally used, which might partially explain the inconsistency.

Original languageEnglish
Pages (from-to)12050-12059
Number of pages10
JournalBiochemistry
Volume45
Issue number39
DOIs
StatePublished - 3 Oct 2006

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    Thoren, K. L., Connell, K. B., Robinson, T. E., Shellhamer, D. D., Tammaro, M. S., & Gindt, Y. M. (2006). The free energy of dissociation of oligomeric structure in phycocyanin is not linear with denaturant. Biochemistry, 45(39), 12050-12059. https://doi.org/10.1021/bi061140+