NMR unfolding studies on a liver bile acid binding protein reveal a global two-state unfolding and localized singular behaviors |
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Authors: | D'Onofrio Mariapina Ragona Laura Fessas Dimitrios Signorelli Marco Ugolini Raffaella Pedò Massimo Assfalg Michael Molinari Henriette |
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Affiliation: | a Dipartimento Scientifico e Tecnologico, Strada le Grazie 15, Università degli Studi di Verona, 37134 Verona, Italy b Laboratorio NMR-ISMAC, CNR, Via Bassini 15, 20133 Milano, Italy c Università di Milano DiSTAM, Via Celoria 2, 20133 Milano, Italy |
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Abstract: | The folding properties of a bile acid binding protein, belonging to a subfamily of the fatty acid binding proteins, have been here investigated both by hydrogen exchange measurements, using the SOFAST NMR approach, and urea denaturation experiments. The urea unfolding profiles of individual residues, acting as single probes, were simultaneously analyzed through a global fit, according to a two-state unfolding model. The resulting conformational stability ΔGU(H2O) = 7.2 ± 0.25 kcal mol−1 is in good agreement with hydrogen exchange stability ΔGop. While the majority of protein residues satisfy this model, few amino-acids display a singular behavior, not directly amenable to the presence of a folding intermediate, as reported for other fatty acid binding proteins. These residues are part of a protein patch characterized by enhanced plasticity. To explain this singular behavior a tentative model has been proposed which takes into account the interplay between the dynamic features and the formation of transient aggregates. A functional role for this plasticity, related to translocation across the nuclear membrane, is discussed. |
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Keywords: | Urea unfolding Nuclear magnetic resonance Chicken liver bile acid binding protein Hydrogen exchange Differential scanning calorimetry Transient aggregation Residual structure |
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