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Reversible denaturation of Brazil nut 2S albumin (Ber e1) and implication of structural destabilization on digestion by pepsin

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Author: Koppelman, S.J. · Nieuwenhuizen, W.F. · Gaspari, M. · Knippels, L.M.J. · Penninks, A.H. · Knol, E.F. · Hefle, S.L. · Jongh, H.H.J.de
Type:article
Date:2005
Institution: TNO Kwaliteit van Leven
Source:Journal of Agricultural and Food Chemistry, 1, 53, 123-131
Identifier: 238305
doi: doi:10.1021/jf0491355
Keywords: Health Toxicology · Food technology · Allergenicity · Denaturation · Pepsin · Protein folding · Protein stability · albumin · guanidine · pepsin A · alkylation · allergenicity · alpha helix · article · Brazil nut · chemical procedures · circular dichroism · energy · food composition · gel electrophoresis · gel permeation chromatography · infrared spectroscopy · mass spectrometry · pH measurement · protein degradation · protein denaturation · protein folding · protein stability · protein structure · temperature dependence · Albumins · Bertholletia · Pepsin A · Plant Proteins · Protein Denaturation · Protein Precursors · Bertholletia excelsa · Ziziphus mauritiana

Abstract

The high resistance of Brazil nut 2S albumin, previously identified as an allergen, against proteolysis by pepsin was examined in this work. Although the denaturation temperature of this protein exceeds the 110 °C at neutral pH, at low pH a fully reversible thermal denaturation was observed at ∼82 °C. The poor digestibility of the protein by pepsin illustrates the tight globular packing. Chemical processing (i.e., subsequent reduction and alkylation of the protein) was used to destabilize the globular fold. Far-UV circular dichroism and infrared spectroscopy showed that the reduced and alkylated form had lost its β-structures, whereas the α-helix content was conserved. The free energy of stabilization of the globular fold of the processed protein as assessed by a guanidine titration study was only 30-40% of that of the native form. Size exclusion chromatography indicated that the heavy chain lost its globular character once separated from the native 2S albumin. The consequences of these changes in structural stability for degradation by pepsin were analyzed using gel electrophoresis and mass spectrometry. Whereas native 2S albumin was digested slowly in 1 h, the reduced and alkylated protein was digested completely within 30 s. These results are discussed in view of the potential allergenicity of Brazil nut 2S albumin.