Fluctuation-Dominated Ligand Binding in Molten Globule Protein

Area of Science:

• Protein dynamics and ligand interactions.
• Biophysics of protein folding intermediates.
• Molecular recognition in biological systems.

Background:

• The molten globule (MG) state is a key intermediate in protein folding.
• Milk protein α-lactalbumin (aLA) forms a complex with oleic acid (OLA) in the MG state, known as XAMLET.
• XAMLET exhibits cytotoxic activity against cancer cell lines, but its binding mechanism is poorly understood.

Purpose of the Study:

• To investigate the microscopic details of ligand recognition in the MG state of aLA.
• To explore the binding of bovine aLA with OLA using computational methods.
• To understand the thermodynamics and dynamics of the MG-aLA-OLA interaction.

Main Methods:

• All-atom molecular dynamics (MD) simulations were employed to study the binding of aLA and OLA.
• Conformational thermodynamics was used to determine the binding mode between MG-aLA and OLA.
• Umbrella sampling (US) and steered MD were utilized to estimate binding free energy and characterize ligand dissociation dynamics.

Main Results:

• The binding mode between MG-aLA and OLA was elucidated using conformational thermodynamics.
• Binding free energy calculations using US showed good agreement with experimental data.
• Steered MD revealed energy fluctuation transfer from the ligand binding site to the Ca2+-binding site during OLA release.

Conclusions:

• This study provides a microscopic understanding of OLA binding to aLA in the MG state.
• The computational approach successfully characterized the binding thermodynamics and dynamics.
• Findings contribute to understanding the XAMLET complex's mechanism of action and potential therapeutic applications.