Structural insights into the high-affinity IgE receptor FcεRI complex

Area of Science:

• Structural Biology
• Immunology
• Molecular Biology

Background:

• Immunoglobulin E (IgE) mediates allergic responses via the high-affinity IgE receptor (FcεRI) on mast cells and basophils.
• FcεRI is a tetrameric complex (FcεRIα, FcεRIβ, FcRγ dimer) crucial for IgE effector functions and signal transduction.
• The Fc receptor gamma (FcRγ) subunit is vital for FcεRI assembly and also part of other immune receptors (FcγRI, FcγRIIIA, FcαRI).

Purpose of the Study:

• To elucidate the molecular basis of FcεRI assembly and the structure of the FcRγ subunit.
• To determine the cryo-electron microscopy (cryo-EM) structure of the Fcε-FcεRI complex.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) to determine the structure of the Fcε-FcεRI complex.
• Mutagenesis analyses to investigate subunit interactions.

Main Results:

• The Fcε-FcεRI complex structure reveals FcεRIα's essential role in assembling FcεRIβ and the FcRγ dimer.
• FcεRIβ forms a compact four-helix bundle; the FcRγ dimer has an asymmetric architecture and forms a three-helix bundle with FcεRIα's transmembrane region.
• A cholesterol-like molecule stabilizes FcεRIβ interaction with the FcεRIα-FcRγ complex; FcRγ interactions show similarities with FcγRIIIA but differences with FcαRI.

Conclusions:

• The study provides the first structural insights into FcεRI assembly and the FcRγ subunit.
• Findings enhance understanding of FcεRI signaling mechanisms in allergic responses.
• The structural data offers insights into the broader functionality of FcRγ-dependent immune receptors.