Soluble immunoglobulin M (IgM) is a pentamer in humans. It triggers a variety of immune responses. IgM is important in the body’s response to a range of foreign pathogens, including cancer cells. But it is also implicated in pathogenesis of autoimmune diseases such as arthritis. Despite IgM’s importance, the detailed structure of human IgM and corresponding detailed mechanism of action are controversial.
Recently, a team at the University of Tokyo used single particle negative–stain electron microscopy to image IgM. The images show the five IgGs arranged in an asymmetric pentamer with an open cleft of about 50 degrees, held open by the J chain polypeptide.
Images in the original article in Science Advances1 clearly show the cleft, which is important in transporting a single circulating apoptosis inhibitor of macrophage (AIM or CD5L). This is responsible for IgM’s therapeutic effectiveness. The authors note that these images are significantly different than cartoons in textbooks. To view images, click here.
This is but one more example of the tremendous improvement in imaging of natural products.
Reference
- Hiramotto, E.; Tsutsumi, A. et al. The IgM pentamer is an asymmetric pentagon with an open groove that binds AIM protein. Science Advances Oct 2018, 4(10), eaau1199; DOI: 10.1126/sciadv.aau1199.
Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]
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