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FcRL4 is an IgA receptor that primarily binds the joining chain

Chen Su1, Yuxin Wang1, Mingqi Zhu1

  • 1Biomedical Pioneering Innovation Center, School of Life Sciences, State Key Laboratory of Gene Function and Modulation Research, Peking University, Beijing 100871, People's Republic of China.

Proceedings of the National Academy of Sciences of the United States of America
|June 17, 2026
PubMed

Insights

Fc-receptor-like 4 (FcRL4) binds Immunoglobulin A (IgA) via its J-chain. Structural and functional studies reveal FcRL4

Area of Science:

  • Immunology
  • Structural Biology
  • Molecular Mechanisms

Background:

  • Immunoglobulin A (IgA) plays a vital role in immune regulation.
  • Fc-receptor-like 4 (FcRL4) is identified as a specific receptor for IgA.
  • The precise molecular basis of FcRL4-IgA interaction was previously unknown.

Purpose of the Study:

  • To elucidate the molecular mechanism by which FcRL4 binds to IgA.
  • To determine the structural basis of FcRL4's selectivity for IgA.
  • To understand the functional implications of the FcRL4-IgA interaction.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to determine the complex structure.
  • Biochemical assays to assess binding interactions.
  • Functional assays to evaluate FcRL4's cellular activities.

Main Results:

  • A 1:1 stoichiometry complex of FcRL4 with the dIgA core (Fcα dimer and J-chain) was resolved.
  • FcRL4 primarily interacts with the J-chain, explaining selective IgA binding.
  • FcRL4 cannot internalize IgA or IgA immune complexes, and secretory component prevents binding to secretory IgA.

Conclusions:

  • The study provides the first structural insights into FcRL4-IgA binding.
  • FcRL4's interaction mechanism and selectivity are clarified.
  • These findings advance the understanding of IgA biology and immune receptor function.

Keywords:
Fc receptorIgAantibody internalizationcryo-EM

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