Human class II MHC molecule HLA-DR1: X-ray structure determined from three crystal forms

Area of Science:

• Structural Biology
• Immunology
• Biochemistry

Background:

• Major histocompatibility complex (MHC) class II molecules present peptides to T cells, playing a crucial role in immune responses.
• Human leukocyte antigen DR1 (HLA-DR1) is a key MHC class II molecule involved in antigen presentation.
• Understanding the three-dimensional structure of HLA-DR1 is essential for deciphering its function in immune recognition.

Purpose of the Study:

• To determine the high-resolution three-dimensional structure of the extracellular region of HLA-DR1.
• To investigate the structural basis of HLA-DR1 complex formation with peptides and superantigens.
• To elucidate the molecular interactions governing antigen presentation by HLA-DR1.

Main Methods:

• X-ray crystallography was employed to determine the structure of HLA-DR1 using three different crystal forms.
• Phasing techniques, including single-isomorphous replacement, were used to generate electron-density maps.
• Non-crystallographic real-space averaging and synchrotron radiation were utilized to achieve a 3.3 A resolution structure.

Main Results:

• The three-dimensional structure of the extracellular region of HLA-DR1 was determined at 3.3 A resolution.
• The structure revealed the binding of endogenous peptides and Staphylococcus aureus enterotoxin B (SEB) to HLA-DR1.
• A parallel dimer of the DR1 alpha-beta heterodimer was observed in the crystal structures.

Conclusions:

• The determined structure provides detailed insights into the molecular architecture of HLA-DR1.
• This structural information facilitates understanding of how HLA-DR1 interacts with various ligands, including peptides and superantigens.
• The findings contribute to the comprehension of T cell recognition and immune system regulation.