Pressure denaturation of β‐lactoglobulin

• DOI: 10.1046/j.1432-1327.2000.01226.x
• Publication Date: 2003-03-11T18:06:15Z
• Authors: Michelle M. Botelho; Vera L. Valente‐M...; Kesley M. G. Oliv...; Igor Polikarpov; Sérgio T. Ferreira
• Keywords: Beta-lactoglobulin; Hydrostatic pressure; Denaturation (fissile materials); Alanine; Mole

Beta-lactoglobulin, the main whey protein in bovine milk, exists several isoforms of which most abundant are A and B. We have previously reported denaturation beta-lactoglobulin by hydrostatic pressure [Valente-Mesquita, V.L., Botelho, M.M. & Ferreira, S.T. (1998) Biophys. J. 75, 471-476]. Here, we compare stabilities These differ two amino-acid substitutions: Asp64 Val118 isoform replaced glycine alanine, respectively, Replacement buried residue smaller alanine side-chain is not accompanied significant structural rearrangements neighbouring polypeptide chain creates a cavity core beta-lactoglobulin. Pressure experiments revealed different isoforms. Standard volume changes (DeltaVunf) - 49 +/- 8 mL.mol-1 -75 3 mL.mol-1, unfolding free energy (DeltaGunf) 8.5 1.3 kJ.mol-1 11.3 0.4 were obtained for B, respectively. The occupied methyl groups removed V118A substitution approximately 40 A3 per monomer beta-lactoglobulin, excellent agreement with experimentally measured difference DeltaVunf (DeltaDeltaVunf = 26 corresponding to 43 monomer). Thus, existence B may explain its enhanced sensitivity relative A. beta-Lactoglobulin undergoes reversible pH-induced conformational change around pH 7, known as Tanford transition. compared at 7 8. Unfolding 8.3 0.3 8, showing that thermodynamic stability identical these values. Interestingly, was dependent on pH, varied from -49 -68 2 large increase appears be associated an overall expansion structure could increased alkaline pH.