An N-linked glycan modulates the interaction between the CD1d heavy chain and beta 2-microglobulin

Area of Science:

• Immunology
• Molecular Biology
• Protein Biochemistry

Background:

• Human CD1d molecules are crucial for presenting lipid antigens to NKT cells.
• CD1d assembly involves heavy chain folding and association with beta(2)-microglobulin in the endoplasmic reticulum.
• N-linked glycans on the CD1d heavy chain are potential modulators of assembly and function.

Purpose of the Study:

• To determine the role of individual N-linked glycans on the human CD1d heavy chain in the assembly and function of CD1d-beta(2)m heterodimers.
• To investigate the impact of glycan mutations on CD1d molecule stability and antigen presentation.

Main Methods:

• Site-directed mutagenesis of N-linked glycosylation sites on the human CD1d heavy chain.
• Analysis of CD1d-beta(2)m heterodimer assembly and stability using biochemical assays.
• Assessment of alpha-galactosyl ceramide binding and presentation to human NKT cells.
• Expression analysis of wild-type and mutant CD1d molecules.

Main Results:

• None of the four N-linked glycans were essential for CD1d-beta(2)m heterodimer assembly or the presentation of alpha-galactosyl ceramide to NKT cells.
• Mutation of glycan 2 at Asn-42 significantly affected CD1d-beta(2)m heterodimer stability, leading to faster ER transport and increased dissociation from beta(2)m.
• A mutant expressing only glycan 2 demonstrated enhanced stability compared to a mutant expressing only glycan 1, suggesting a specific role for glycan 2.

Conclusions:

• While not essential for basic assembly or antigen presentation, specific N-linked glycans, particularly glycan 2, play a critical role in stabilizing the human CD1d-beta(2)m heterodimer.
• Glycan 2's interaction with both the CD1d heavy chain and beta(2)-microglobulin likely contributes to heterodimer stability.
• Understanding glycan roles in CD1d assembly provides insights into immune response modulation.