Effect of hydrophobicity on protein-protein interactions

A comparative study of the effect of protein hydrophobicity on the protein-protein interactions is reported here. The bindings of trypsin with model proteins of different hydrophobic characters such as human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) were investigated in aqueous solution, using multiple spectroscopic methods and thermodynamic analysis. Hydrophobicity played a major role in protein-protein interactions with more hydrophobic b-LG forming stronger trypsin-protein complexes with the binding constants of KTrypsin-b-LG- = 9.8 x 10(4) M-1, KTrypnsin-BSA- = 4.1 x 10(4) M-1 and KTrypsin-HSA- = 3.1 x 10(4) M-1. Thermodynamic analysis with Delta S 74 to -21 (J Mol(-1) K-1), Delta H -10000 to -900 (kJ Mol(-1) K-1) and Delta G -1000 to -900 (kJ Mol(-1) K-1) showed trypsin-protein bindings occur via hydrophobic and H-bonding contacts for HSA and BSA, while van der Waals and H-bonding interactions prevail in trypsin-b-LG adducts. Trypsin complexation induced major alterations of b-LG conformation and minor changes of HSA and BSA secondary structures. (C) 2015 Elsevier Ltd. All rights reserved.