Characterization of the IgE receptor by tryptic mapping

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• The immunoglobulin E (IgE) receptor plays a crucial role in allergic responses.
• Understanding the structural and membrane orientation of the IgE receptor is essential for elucidating its function.

Purpose of the Study:

• To characterize the IgE receptor on rat basophilic leukemia (RBL) cells and rat peritoneal mast cells (RMC).
• To determine the membrane orientation and potential transmembrane nature of the IgE receptor.

Main Methods:

• Surface radioiodination of IgE receptors on intact cells and membrane particles.
• Immunoprecipitation of IgE-receptor complexes using anti-rat IgE.
• Purification by SDS-PAGE and affinity chromatography (IgE-Sepharose).
• Tryptic digestion and 2-dimensional peptide mapping analyzed by autoradiography.

Main Results:

• IgE receptors from different RBL cell lines and RMC showed identical tryptic peptide maps, despite minor molecular weight differences.
• A distinct higher molecular weight IgE-binding component was identified and found on all tested cell types.
• Tryptic mapping of receptors labeled at different cellular locations indicated labeling was restricted to the surface-exposed IgE binding site.
• Saturation of the receptor by IgE blocked subsequent radioiodination, confirming labeling specificity.

Conclusions:

• The IgE receptor on RBL cells and RMC appears to be primarily located on the cell surface.
• Labeling patterns suggest the IgE receptor is not a transmembrane protein, with accessible labeling sites limited to the IgE binding domain.