Structural insights into immunoglobulin M

Science. 2020 Feb 28;367(6481):1014-1017. doi: 10.1126/science.aaz5425. Epub 2020 Feb 6.


Immunoglobulin M (IgM) plays a pivotal role in both humoral and mucosal immunity. Its assembly and transport depend on the joining chain (J-chain) and the polymeric immunoglobulin receptor (pIgR), but the underlying molecular mechanisms of these processes are unclear. We report a cryo-electron microscopy structure of the Fc region of human IgM in complex with the J-chain and pIgR ectodomain. The IgM-Fc pentamer is formed asymmetrically, resembling a hexagon with a missing triangle. The tailpieces of IgM-Fc pack into an amyloid-like structure to stabilize the pentamer. The J-chain caps the tailpiece assembly and bridges the interaction between IgM-Fc and the polymeric immunoglobulin receptor, which undergoes a large conformational change to engage the IgM-J complex. These results provide a structural basis for the function of IgM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • Humans
  • Immunoglobulin Fc Fragments / chemistry
  • Immunoglobulin Fc Fragments / immunology
  • Immunoglobulin J-Chains / chemistry
  • Immunoglobulin J-Chains / immunology
  • Immunoglobulin M / chemistry*
  • Immunoglobulin M / immunology*
  • Protein Conformation
  • Protein Multimerization
  • Receptors, Polymeric Immunoglobulin / chemistry*


  • Immunoglobulin Fc Fragments
  • Immunoglobulin J-Chains
  • Immunoglobulin M
  • Receptors, Polymeric Immunoglobulin
  • polymeric IgM