Mapping the Binding Hot Spots on Human Programmed Cell Death 1 and Its Ligand with Free-Energy Simulations

Area of Science:

• * Molecular biology
• * Computational biophysics
• * Immunology

Background:

• * The human programmed cell death 1 (hPD-1) and human programmed cell death ligand 1 (hPD-L1) pathway is a critical immune checkpoint targeted in cancer therapy.
• * Blocking the hPD-1/hPD-L1 interaction shows therapeutic promise, but the specific residues driving this interaction are not fully understood.
• * Existing crystallographic data offer static views, necessitating dynamic analysis to identify key binding residues.

Purpose of the Study:

• * To computationally identify and characterize the hot spot residues responsible for the binding affinity between hPD-1 and hPD-L1.
• * To investigate the distribution and energetic contributions of these critical residues.
• * To elucidate the binding mechanism from a biophysical perspective.

Main Methods:

• * Alchemical free-energy simulations were employed to calculate the energetic contributions of interfacial residues.
• * Analysis focused on identifying residues with significant impact on the hPD-1/hPD-L1 binding process.
• * The spatial distribution and polarity of hot spot residues were examined.

Main Results:

• * Specific hot spot residues on hPD-1 (Tyr68, Gln75, Ile126, Leu128, Ile134, Glu136) and hPD-L1 (Asp26, Ile54, Tyr56, Met115, Asp122, Tyr123, Lys124) were identified.
• * These hot spot residues are unevenly distributed, with key residues concentrated in hydrophobic regions.
• * The binding mechanism was analyzed through the lens of the O-ring theory.

Conclusions:

• * This study pinpoints critical residues governing hPD-1/hPD-L1 interaction, essential for understanding immune checkpoint regulation.
• * The findings provide valuable insights for designing targeted anticancer inhibitors.
• * Computational methods offer a powerful approach to dissecting protein-protein interactions in drug discovery.