Effect of hydrophobicity on protein–protein interactions

• The effect of hydrophobicity on protein–protein interactions is investigated.
• Trypsin–protein bindings are via hydrophobic, H-bonding and van der Waals.
• More hydrophobic b-LG forms more stable complexes than HSA and BSA.
• Protein–protein interactions alter protein conformation.

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 × 104 M−1, KTrypsin–BSA- = 4.1 × 104 M−1 and KTrypsin–HSA- = 3.1 × 104 M−1. Thermodynamic analysis with ΔS 74 to −21 (J Mol−1 K−1), ΔH −10000 to −900 (kJ Mol−1 K−1) and ΔG −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.

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