pH and heat-induced structural changes of bovine apo-α-lactalbumin

The effects of pH and thermal treatments on conformation and association state of Ca2+-depleted bovine α-lactalbumin (apo-α-LA) have been studied by fluorescence spectroscopy, and molecular modelling. The experimental results demonstrate a third-state model for heat-induced unfolding of apo-α-LA, at pH 2.0, and an all-or-none transition of apo-α-LA, at pH 4.5 and 7.0, respectively. The heat-induced changes in the secondary and tertiary structure of α-LA were outlined after running molecular dynamics simulations at 25 °C and 80 °C, at neutral pH, therefore supporting the experimental observations. Our data provides insight into the mechanism of pH- and heat-dependent structural changes and oligomerization of α-LA, and will be helpful in understanding the ability of this protein to interact with certain compounds of biological interest.

► In this study, we monitor the conformational changes of α-LA induced by pH and heat treatment. ► The heat-induced denaturation of α-LA at pH 2.0 was a third-state model. ► Heat treatment caused a decrease of the intrinsic fluorescence and an increase of the ANS fluorescence. ► The conformational changes involved mainly α and 310 helices and beta turns. ► Based on the KSV values, a significant increase in accessibility of Trp at pH 2.0 was reported.