Lipopeptide ligands captured by MHC class I molecules undergo dynamic conformational changes that affect their...

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Major histocompatibility complex (MHC) class I molecules present peptides to T cells, typically longer peptides.
• A subset of MHC class I molecules can present N-myristoylated short lipopeptides, such as those derived from retroviral Nef protein.
• The interaction involves specific MHC class I allomorphs, like Mamu-B*05104, and T-cell receptors (TCRs).

Purpose of the Study:

• To elucidate the molecular mechanisms governing the antigenic strength of N-myristoylated lipopeptides.
• To understand why lipopeptides sharing a primary T-cell epitope can be either antigenic or nonantigenic.
• To investigate the structural basis for differential T-cell recognition of lipopeptide antigens.

Main Methods:

• Utilized N-myristoylated 4-mer lipopeptides (C14nef4) and their analogs with amino acid substitutions.
• Employed biolayer interferometry to measure the binding affinity between immobilized TCRs and Mamu-B*05104-lipopeptide complexes.
• Determined crystal structures of Mamu-B*05104 complexed with various lipopeptides and performed molecular dynamics simulations.

Main Results:

• Both the myristic acid and C-terminal residues of C14nef4 anchor in the MHC binding groove, exposing internal residues like Gly1.
• The amide bond of Gly1 serves as the primary T-cell epitope, but its accessibility varies.
• Poorly antigenic lipopeptide analogs exhibited a downward shift in the hydrocarbon chain and Gly1, reducing epitope exposure.
• Molecular dynamics simulations confirmed that lipopeptide conformation dynamically affects the external presentation of the Gly1 epitope.

Conclusions:

• The antigenic strength of N-myristoylated lipopeptides is determined by their intrinsic conformational flexibility.
• Lipopeptides that maintain an exposed T-cell epitope conformation are more antigenic.
• This conformational plasticity explains the differential immune recognition of lipopeptides with shared T-cell epitopes.