Biphasic transition curve on denaturation of chicken cystatin by guanidinium chloride. Evidence for an independently unfolding structural region. |
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Authors: | I Bj?rk E Pol |
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Institution: | Department of Veterinary Medical Chemistry, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, Sweden. |
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Abstract: | Far-ultraviolet circular dichroism and tryptophan fluorescence measurements showed that the reversible unfolding of the cysteine proteinase inhibitor, chicken cystatin, by guanidinium chloride is a two-step process with transition midpoints at approximately 3.4 and approximately 5.4 M denaturant. The partially unfolded intermediate had both far- and near-ultraviolet circular dichroism and fluorescence emission spectra comparable to those of the native protein. The largely retained tertiary structure suggests that the intermediate represents a species in which a separate region of lower stability has been unfolded, rather than an intermediate of the 'molten globule' type. Such a structurally independent region is apparent in the three-dimensional structure of the inhibitor. |
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