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Changes in Structure and in Interactions of Heat-Treated Bovine β-Lactoglobulin

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Heat stress on structure and ligand binding of β-LG has been studied by fluorescence, circular dichroism and gel electrophoresis at pH 6.5. Native PAGE gel electrophoresis shows that denaturation of β-LG is reversible up to 75°C then it becomes irreversible due to aggregation of β-LG. Formation of aggregated β-LG is completed at 95°C. Circular dichroism results indicate that formation of aggregated β-LG is accompanied by the scrambling of disulfide bonds (creation of new intramolecular and intermolecular disulfide bridges and rearrangement of old intramolecular disulfide bridges). Addition of ethanolic retinol causes a change in polarity of the solution and favors transformation of the β↔α structure. In the presence of retinol, the β-helix content of the secondary structure of heat-treated β-LG is increased and the major portion of its secondary structure is helical. Fluorescence results show that heat-treated β-LG at 95°C can still bind retinol. The refolding of the tertiary structure of β-LG heat-denatured at 95°C may recreate a retinol binding site. Surprisingly, the affinity of the new site for retinol is higher than that of native β-LG; however, the apparent molar ratio is lower than one. The binding properties of β-LG for terpenoids have been measured after its heat treatment at 20, 75 and 95°C. The intensity of tryptophan emission at 330 nm was changed only in the case of the interaction with β-ionone. Other ligands probably cannot bind to β-LG or they bind in a binding site far from the tryptophan residues, hence not affecting its fluorescence.

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Keywords: circular dichroism; fluorescence; gel electrophoresis; retinol; terpenes; β-lactoglobulin

Document Type: Research Article

Publication date: 2008-08-01

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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