Elucidating Ligand Charge Effects in MR1 Cell-Surface Translocation Using Molecular Simulations

Area of Science:

• Immunology
• Structural Biology
• Computational Chemistry

Background:

• The major histocompatibility complex class I-related protein 1 (MR1) presents ligands to mucosal-associated invariant T (MAIT) cells, influencing immune responses.
• MAIT cells are vital for infection defense and tissue repair but are also implicated in various diseases.
• Understanding MR1-ligand interactions is key, as MR1 cell surface levels vary significantly based on its ligands, yet the binding mechanism and structure-activity relationships are poorly understood.

Purpose of the Study:

• To elucidate the chemical properties of MR1 ligands that regulate cell surface MR1 levels.
• To investigate the interaction mechanism between MR1 and its ligands using computational methods.
• To determine the stability of MR1-ligand complexes and identify key factors influencing MR1 cell surface expression.

Main Methods:

• Computational analysis of MR1-ligand interactions.
• Determination of MR1-ligand complex stability.
• Analysis of ligand chemical properties and their impact on MR1 cell surface levels.

Main Results:

• MR1 binds both covalent and noncovalent ligands in an anionic state, contrary to previous assumptions of a neutral state.
• The binding of anionic ligands stabilizes the MR1-ligand complex.
• Neutralization of the positive charge from Arg9 by anionic ligands is a critical factor enhancing MR1 cell surface levels.

Conclusions:

• MR1 ligand binding occurs in an anionic state, stabilizing the complex and enhancing cell surface expression.
• The findings clarify the molecular basis for MR1 regulation by its ligands.
• This study provides a foundation for designing novel ligands to modulate MAIT cell activation.