Molecular basis of human CD22 function and therapeutic targeting

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• CD22 is a B-cell-specific co-receptor crucial for maintaining humoral immunity.
• Dysregulated B cells contribute to autoimmune diseases and blood cancers, making CD22 a therapeutic target.

Purpose of the Study:

• To determine the crystal structure of human CD22 and elucidate its ligand-binding mechanism.
• To structurally characterize the binding site of the therapeutic antibody epratuzumab on CD22.
• To gain molecular insights into B-cell inhibition mediated by CD22.

Main Methods:

• X-ray crystallography was used to determine the structure of human CD22 at 2.1 Å resolution.
• The structure of CD22 bound to the therapeutic antibody epratuzumab was determined at 3.1 Å resolution.

Main Results:

• The CD22 structure reveals a unique β-hairpin mechanism for recognizing α2-6 sialic acid ligands.
• The ectodomain adopts an extended conformation, facilitating B-cell nanocluster formation and trans-ligand binding.
• A critical role for CD22 N-linked glycosylation in antibody engagement was identified.

Conclusions:

• The findings provide a molecular understanding of CD22's role in B-cell inhibition and autoimmunity prevention.
• Structural insights into CD22-epratuzumab interaction offer valuable guidance for designing novel immune modulators for B-cell dysfunction.