Molecular Basis for the Differential Function of HAVCR1 Mucin Variants

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Hepatitis A virus cellular receptor 1 (HAVCR1) is a glycoprotein involved in viral entry and immune responses.
• HAVCR1 has an immunoglobulin-like variable domain (IgV) that binds phosphatidylserine on apoptotic cells, extracellular vesicles, and enveloped viruses.
• Genetic variations (156ins/del) in the mucin-like domain (Muc) of HAVCR1 are linked to various diseases, but their functional impact is unclear.

Purpose of the Study:

• To investigate the molecular mechanisms by which the 156ins/del variations in HAVCR1 affect its function.
• To understand how these variations influence HAVCR1 binding, signaling, and phagocytosis.

Main Methods:

• Site-directed mutagenesis was employed to create HAVCR1 variants with and without the 156 insertion.
• Apoptotic cell binding assays were performed to quantify the interaction of HAVCR1 variants with apoptotic cells.
• Signal transduction and phagocytosis assays were conducted to assess the functional consequences of the variations.

Main Results:

• The HAVCR1 variant lacking the 156 insertion (short-HAVCR1) exhibited enhanced binding to apoptotic cells compared to the variant with the insertion (long-HAVCR1).
• Short-HAVCR1 demonstrated stronger induction of cell signaling and phagocytosis than long-HAVCR1.
• The 156ins/del variations dictate the presentation of the IgV domain on the cell surface.

Conclusions:

• The 156ins/del variations in HAVCR1 significantly modulate its binding affinity, signaling capacity, and phagocytic activity.
• These findings suggest that the structural presentation of the IgV domain is critical for HAVCR1 function.
• Targeting specific HAVCR1 variants could offer novel therapeutic strategies for immune and infectious diseases.