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

H-1 NMR was used to study the effect of high pressure on changes in the str ucture of beta-lactoglobulin (beta-Lg), particularly the strongly bonded re gions, 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 deuteriu m exchange. Refolding was also evaluated. Our results showed that the core was unaltered at 100 MPa but increased its conformational. flexibility at g reater than or equal to 200 MPa. Even though the core was highly flexible a t 400 MPa, its structure was found to be identical to the native structure after equilibration back to atmospheric pressure. It is suggested that pres sure-induced aggregates are formed by beta-Lg molecules maintaining most of their structure, and the intermolecular -SS- bonds, formed by -SH/-SS- exc hange reaction, are likely to involve C-66-C-160 rather than C-106-C-119. I n addition, the beta-Lg variants A and B could be distinguished in a H-1 NM R spectrum from a solution made with the AB mixed variant, by the differenc es in chemical shifts of M-107 and C-106; structural implications are discu ssed. Under pressure, the core of beta-Lg A seemed to unfold faster than th at of beta-LgB. The structural recovery of the core was full for both varia nts.