Structure of a classical MHC class I molecule that binds "non-classical" ligands

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Chicken YF1 genes are similar to classical Major Histocompatibility Complex (MHC) class I loci but located outside the core MHC region.
• Understanding the function of these YF1 genes is crucial for avian immunology.

Purpose of the Study:

• To determine the structure of the YF1*7.1/β(2)-microglobulin complex.
• To investigate the binding capabilities of YF1*7.1 with various ligands, particularly hydrophobic ones.

Main Methods:

• X-ray crystallography was used to determine the structure of the YF1*7.1/β(2)-microglobulin complex at 1.3 Å resolution.
• Reconstitution experiments were performed with YF1*7.1 and various self-lipids.
• Native isoelectric focusing was employed to assess YF1*7.1 binding with nonself-lipids.

Main Results:

• The YF1*7.1/β(2)-microglobulin complex displays a typical MHC class I architecture.
• A hydrophobic binding groove was identified, capable of accommodating non-peptidic ligands, including polyethyleneglycol.
• YF1*7.1 demonstrated the ability to bind nonself-lipids, a function not observed in classical MHC class I proteins.

Conclusions:

• Chicken YF1*7.1 exhibits an unprecedented ability to interact with hydrophobic ligands, including lipids.
• This unique characteristic may enable the chicken immune system to recognize a broader range of ligands using a limited set of MHC class I molecules.