Water dynamics at the binding interface of four different HLA-A2-peptide complexes

Area of Science:

• Immunology
• Structural Biology
• Computational Biology

Background:

• Major histocompatibility complex (MHC) molecules present peptides to T cells, a critical immune function.
• MHC molecules must bind a wide range of peptides with sufficient affinity for stable presentation.
• The precise mechanism facilitating promiscuous peptide binding in MHC molecules remains an area of investigation.

Purpose of the Study:

• To investigate the role of water molecules in the peptide-binding groove of the human leukocyte antigen (HLA) molecule HLA-A2.
• To understand how water networks influence the binding affinity and stability of diverse peptide complexes with HLA-A2.

Main Methods:

• Utilized X-ray crystallography to determine the structures of HLA-A2 complexed with four different peptides.
• Employed the SURFNET program to analyze the 'gaps' and water-binding sites within the peptide-binding groove.
• Performed molecular dynamics simulations to observe the behavior and dynamics of water molecules at the MHC-peptide interface.

Main Results:

• The volume of gaps in the HLA-A2 peptide-binding groove correlated with peptide hydrophilicity.
• Hydrophilic peptides exhibited disordered water molecules in the binding groove, with some defined water-binding sites.
• Hydrophobic peptides showed more rigidly bound water molecules and well-defined, albeit dynamic, water-binding sites at the MHC-peptide interface.

Conclusions:

• A flexible water network at the interface between HLA-A2 and bound peptides may facilitate promiscuous peptide binding.
• The dynamics and structure of water molecules in the binding groove are influenced by peptide hydrophilicity.
• Understanding these water-mediated interactions could offer insights into immune recognition and T-cell activation.