Bovine β-lactoglobulin, an abundant protein in whey, is a promising nanocarrier for peroral administration of drug-like hydrophobic molecules, a process that involves transit through the different acidic conditions of the human digestive tract. Among the several pH-induced conformational rearrangements that this lipocalin undergoes, the Tanford transition is particularly relevant. This transition, which occurs with a midpoint around neutral pH, involves a conformational change of the E-F loop that regulates accessibility to the primary binding site. The effect of this transition on the ligand binding properties of this protein has scarcely been explored. In this study, we carried out an energetic and structural characterization of β-lactoglobulin molecular recognition at pH values above and below the zone in which the Tanford transition occurs. The combined analysis of crystallographic, calorimetric, and molecular dynamics data sheds new light on the interplay between self-association, ligand binding, and the Tanford pre- and post-transition conformational states, revealing novel aspects underlying the molecular recognition mechanism of this enigmatic lipocalin.

牛β-乳球蛋白是乳清中的一种丰富蛋白质，是经口给药类药物疏水分子的有前途的纳米载体，该过程涉及通过人类消化道不同酸性条件的转运。在该脂环蛋白经历的几种pH诱导的构象重排中，Tanford转变尤其重要。这种转变发生在中性pH值附近的中点，涉及EF环的构象变化，该变化调节了对主要结合位点的可及性。几乎没有研究过这种转变对该蛋白的配体结合特性的影响。在这项研究中，我们对pH值高于和低于发生Tanford转变的区域进行了β-乳球蛋白分子识别的能量和结构表征。