Trypsin and trypsin inhibitor bind milk beta-lactoglobulin: Protein-protein interactions and morphology

Conjugation of trypsin and trypsin inhibitor with milk beta-lactoglobulin (b-LG) was studied in aqueous solution at physiological pH. Multiple spectroscopic methods and transmission electron microscopy (TEM) were used to characterize protein-protein interactions and protein morphology. Thermodynamic analysis Delta H (-24 to -11 kJ Mol(-1)), Delta S (-30 to -5 J Mol(-1) K-1) and Delta G (-12 to -10 kJ Mol(-1)) showed that protein-protein interactions occur via H-bonding and van der Waals contacts. The binding affinity was trypsin >trypsin inhibitor with Ktrypsin-b-LG = 9.8 (+/- 1) x 10(4) M-1 and Ktrypsininhibitor-b-LG = 7.5 (+/- 0.7) x 10(3) M-1. Transmission electron microscopy showed major changes in protein morphology upon protein-protein interactions. (C) 2017 Elsevier B.V. All rights reserved.