A 1H-NMR study on the effect of high pressures on β-lactoglobulin

H-1 NMR was used to study the effect of high pressure on changes in the structure of beta-lactoglobulin (beta-Lg), particularly the strongly bonded regions, the "core". beta-Lg was exposed to pressures ranging from 100 to 400 MPa at neutral pH. After depressurization and acidification to pH 2.0, H-1 NMR spectra were taken. Pressure-induced unfolding was studied by deuterium exchange. Refolding was also evaluated. Our results showed that the core was unaltered at 100 MPa but increased its conformational. flexibility at greater than or equal to 200 MPa. Even though the core was highly flexible at 400 MPa, its structure was found to be identical to the native structure after equilibration back to atmospheric pressure. It is suggested that pressure-induced aggregates are formed by beta-Lg molecules maintaining most of their structure, and the intermolecular -SS- bonds, formed by -SH/-SS- exchange reaction, are likely to involve C-66-C-160 rather than C-106-C-119. In addition, the beta-Lg variants A and B could be distinguished in a H-1 NMR spectrum from a solution made with the AB mixed variant, by the differences in chemical shifts of M-107 and C-106; structural implications are discussed. Under pressure, the core of beta-Lg A seemed to unfold faster than that of beta-LgB. The structural recovery of the core was full for both variants.