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United States Department of Agriculture

Agricultural Research Service

Title: Stability of the Allergenic Soybean Kunitz Trypsin Inhibitor

Authors
item Roychaudhuri, R - UNI OF NE
item Sarath, Gautam
item Zeece, M - UNI OF NE
item Markwell, J - UNI OF NE

Submitted to: Biochimica et Biophysica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2004
Publication Date: June 1, 2004
Citation: Roychaudhuri, R., Sarath, G., Zeece, M.G., Markwell, J. 2004. Stability of the allergenic soybean kunitz trypsin inhibitor. Biochimica et Biophysica Acta. 699:207-212.

Interpretive Summary: Protein allergens are major antinutritive components of foods. Many protein allergens display resistance to thermal denaturation as well as to the human digestive process. The molecular features that impart this resistance and its relationship to allergenicity are not obvious. Thus work with model proteins can potentially extend our understanding of biophysical and biochemical mechanisms that can impart resistance to thermal and chemical denaturation. In this study we have used the Soybean Kunitz trypsin inhibitor (SKTI) as model protein. SKTI is a 21.5 kDa allergenic protein that belongs to the family of all antiparallel '-sheet proteins. Spectroscopic and biochemical techniques such as CD, ANS fluorescence and proteolysis were used to study its molecular structure under denaturing conditions such as acid and heat to which these allergens are commonly exposed during food processing. Breaking disulfide bonds that exist in native SKTI leads to its complete and rapid proteolysis by pepsin in simulated gastric fluid (SGF). Limited proteolysis with chymotrypsin during renaturation after heating showed that the native structure reforms at around 60°C reversing the denaturation. CD spectra revealed that under acid denaturing conditions (pH 1.2), SKTI shows major changes in the extent of coil structure and its native tertiary structure indicating the possibility of a molten structure. The existence of this intermediate was established by ANS fluorescence studies at different concentrations of HCl and in SGF (without pepsin). The remarkable stability of SKTI to both thermal and acid denaturation may be important for its role as a food allergen.

Technical Abstract: The Soybean Kunitz trypsin inhibitor (SKTI) is a 21.5 kDa allergenic protein that belongs to the family of all antiparallel '-sheet proteins that are highly resistant to thermal and chemical denaturation. Spectroscopic and biochemical techniques such as CD, ANS fluorescence and proteolysis were used to study its molecular structure under denaturing conditions like acid and heat to which these allergens are commonly exposed during food processing. Reduction of native SKTI leads to its complete and rapid proteolysis by pepsin in simulated gastric fluid (SGF). Limited proteolysis with chymotrypsin during renaturation after heating showed that the native structure reforms at around 60°C reversing the denaturation. CD spectra revealed that under acid denaturing conditions (pH 1.2), SKTI shows major changes in the extent of coil structure and its native tertiary structure indicating the possibility of a molten structure. The existence of this intermediate was established by ANS fluorescence studies at different concentrations of HCl and in SGF (without pepsin). The remarkable stability of SKTI to both thermal and acid denaturation may be important for its role as a food allergen.

Last Modified: 4/16/2014
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