The IgM pentamer is an asymmetric pentagon with an open groove that binds the AIM protein.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30324136.
- Also identified by DOI 10.1126/sciadv.aau1199 and PMC identifier 6179379.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Soluble immunoglobulin M (IgM) forms a pentamer containing a joining (J) chain polypeptide. While IgM pentamer has various immune functions, it also behaves as a carrier of circulating apoptosis inhibitor of macrophage (AIM; also called CD5L) protein that facilitates repair during different diseases. AIM binds to the IgM pentamer solely in the presence of the J chain. Here, using a single-particle negative-stain electron microscopy, we found that the IgM pentamer exhibits an asymmetric pentagon containing one large gap, which is markedly different from the textbook symmetric pentagon model. A single AIM molecule specifically fits into the gap, cross-bridging two IgM-Fc that form the edges of the gap through a disulfide bond at one side and a charge-based interaction at the other side. The discovery of the bona fide shape of the IgM pentamer advances our structural understanding of the pentameric IgM and its binding mode with AIM.
Medical subject headings
- Apoptosis Regulatory Proteins
- Cell Membrane
- Immunoglobulin M
- Receptors, Immunologic