The protein dynamics of bovine and caprine β-lactoglobulin differ as a function of pH

The properties of milk proteins differ between mammalian species. beta-Lactoglobulin (beta lg) proteins from caprine and bovine milk are sequentially and structurally highly similar, yet their physicochemical properties differ, particularly in response to pH. To resolve this conundrum, we compared the dynamics of both the monomeric and dimeric states for each homologue at pH 6.9 and 7.5 using hydrogen/deuterium exchange experiments. At pH 7.5, the rate of exchange is similar across both homologues, but at pH 6.9 the dimeric states of the bovine beta lg B variant homologue have significantly more conformational flexibility compared with caprine beta lg. Molecular dynamics simulations provide a mechanistic rationale for the experimental observations, revealing that variant -specific substitutions encode different conformational ensembles with different dynamic properties consistent with the hydrogen/deuterium exchange experiments. Understanding the dynamic differences across beta lg homo-logues is essential to understand the different responses of these milks to processing, human digestion, and differences in immunogenicity.

Automated summary

The properties of milk proteins vary between different mammalian species. This study focuses on comparing the dynamics of beta-lactoglobulin (β lg) proteins from goat and cow milk at different pH levels. The dimeric states of the cow β lg B variant homologue exhibit more conformational flexibility than the goat β lg at lower pH, as observed through hydrogen/deuterium exchange experiments and molecular dynamics simulations. Understanding these dynamic differences in β lg homologues is crucial for understanding the variations in milk processing, human digestion, and immunogenicity.