• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1567-1572
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• 2009

Conformational change of ubiquitin variant with valine to alanine mutation at sequence position 26 was studied by varying solvent pH. Fluorescence emission spectra indicated that this variant ubiquitin has some residual structures in acidic and basic solution as compared to denaturant-induced unfolded state. Far-UV circular dichroic spectra indicated that the base-denatured state had more secondary structure than the acid-denatured state. Near-UV circular dichroic spectra indicated that the aromatic side-chains were in the relatively more rigid environment in the base-denatured state than those in the acid-denatured state. Although it appears that the more tertiary structure present in the base-denatured state, refolding reactions measured by stopped-flow fluorescence device suggest that both the acid- and base-denatured states occur before the major folding transition state. The acid- and base-denatured states are considered to reflect the early event of protein folding process.

• Applied Biological Chemistry
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• v.46 no.4
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• pp.305-310
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• 2003

Hydrophobic core variant of ubiquitin appeared to have partially folded structure at pH around 2. The intrinsic tryptophan fluorescence emission maximum of this ubiquitin variant at pH 2 showed slight blue shift compare to that of unfolded state, suggesting that some residual tertiary structures remain in this solvent condition. At the same solvent condition, this ubiquitin variant binds with hydrophobic dye, 8-anilinonaphthalene-1-sulfonic acid(AMS), which is known to bind to exposed hydrophobic surface. Furthermore, far-UV circular dichroic spectrum of this ubiquitin variant in the diminished pH was remarkably different from the far-UV CD spectrum of the native state or unfolded state. Based on the molar ellipticity at 220 nm, this ubiquitin variant at pH 2 appeared to have significant amount of secondary structures. All these observations suggest that this ubiquitin variant in the diminished solvent pH has loosely folded hydrophobic core with some secondary structures, which are key features of molten globule conformation. Since molten globule has long been considered as a protein folding intermediate, it is considered that this hydrophobic core variant ubiquitin will serve as a valuable model to study protein folding process.

• BMB Reports
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• v.37 no.6
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• pp.676-683
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• 2004

The conformational properties of hydrophobic core variant ubiquitin (Val26 to Ala mutation) in an acidic solution were studied. The intrinsic tryptophan fluorescence emission spectrum, far-UV and near-UV circular dichroic spectra, the fluorescence emission spectrum of 8-anilinonaphthalene-1-sulfonic acid in the presence of V26A ubiquitin, and urea-induced unfolding measurements indicate this variant ubiquitin to be in the partially folded molten globule conformation in solution at pH 2. The folding kinetics from molten globule to the native state was nearly identical to those from the unfolded state to the native state. This observation suggests that the equilibrium molten globule state of hydrophobic core variant ubiquitin is an on-pathway folding intermediate.

• Bulletin of the Korean Chemical Society
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• v.23 no.9
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• pp.1315-1327
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• 2002

The model compounds, 8-methoxypsoralen-CH2O(CH2)n-adenine (MOPCH2OCnAd, n=2, 3, 5, 6, 8, and 10) in which 5 position of 8-methoxypsoralen (8-MOP) is linked by various lengths of polymethylene bridge to N9 of adenine. UV absorption spectra are identical with the sum of MOPCH2OC3 and adenine absorption spectra. Solvent effects on the UV absorption and fluorescence emission spectra indicate that the lowest excited singlet state is the $(\pi${\rightarrow}$\pi*)$ state. The spectral characteristics of the fluorescence of MOPCH2OCnAd are strongly dependent upon the nature of the solvents. The fluorescence emission spectra in aprotic solvents are broad and structureless due to the excimer formation through the folded conformation accelerated by hydrophobic ${\pi}-{\pi}$ stacking interaction. Increasing polarity of the protic solvents leads to higher population of unfolded conformation stabilized through favorable solvation and H-bonding, and consequently to an increase in the fluorescence intensity, fluorescence lifetime, and a shift of fluorescence maximum to longer wavelengths. The decay characteristics of the fluorescence in polar protic solvents shows two exponential decays with the lifetimes of 0.6-0.8 and 1.6-1.9 ns in 5% ethanol/water, while MOPCH2OC3 shows 0.5 and 1.7 ns fluorescence lifetimes. The long-lived component of fluorescence can be attributed to the relaxed species (i.e., the species for which the solvent reorientation (or relaxation) has occurred), while the short-lived components can be associated with the unrelaxed, or only partially relaxed, species.