Influence of binding of sodium dodecyl sulfate, all-trans-retinol, and 8-anilino-1-naphthalenesulfonate on the high-pressure-induced unfolding and aggregation of β-lactoglobulin B

Bovine beta-lactoglobulin B (beta-LG) is susceptible to pressure treatment, which unfolds it, allowing thick catalyzed disulfide bond interchange to occur, facilitating intermolecular bonding (both noncovalent and disulfide). In the present study, beta-LG was mixed with sodium dodecyl sulfate (SIDS), all-transretinol (retinol), or 8-anilino-1-naphthalenesulfonate (ANS) on a 1:1.1 molar basis, and aliquots were held at pressures between 50 and 800 MPa for 30 min at pH 7.2 and 20 degrees C. Polyacrylamide gel electrophoresis (PAGE) showed that beta-LG alone (control) was converted into a non-native monomer and a series of dimers, trimers, etc., at pressures beyond 100 IVIPa; SIDS inhibited the formation of. non-native species up to 200 IVIPa, and neither retinol nor ANS inhibited the formation of the nonnative species as effectively as SIDS. At pressures beyond 350 MPa, SIDS ceased to have any inhibitory effect, but both ANS and retinol showed significant inhibition. The near- and far-UV CID patterns and the ANS fluorescent data were consistent with the PAGE data, but the retinol fluorescent data did not show sufficient change to interpret. The results suggested that there were three discernible structural stages. In Stage 1 (0.1-150 MPa), the native structure is stable; in Stage 11 (200-450 MPa), the native monomer is reversibly interchanging with non-native monomers and disulfide-bonded dimers; and in Stage III (> 500 MPa), the free CysH in non-native monomer and dimer interacts with -S-S- bonds to produce high molecular weight aggregates of beta-LG. SIDS inhibited the Stage I to Stage 11 transition at 200 MPa, and ANS and retinol inhibited the Stage 11 to Stage III transition at 600 MPa.