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Shared parts, different structures: How asymmetry drives IgM and IgA structure-function relationships
Rebecca M Schneider1, Yujia Ji2, Beth M Stadtmueller3
1Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, 61801, USA; Carl R. Woese Institute of Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, 61801, USA.
Polymeric (p) immunoglobulins (Igs) and their secretory (S) forms are critical to vertebrate immunity. The pIgs and SIgs comprise a molecularly diverse family of antibodies that contain multiple Ig monomers, up to one joining chain (JC), and up to one secretory component. A subset of pIgs function in circulation whereas SIgs populate mucosal barriers. The pIgs and SIgs exhibit unique functions compared to monomeric Igs, yet their underlying molecular structures remained largely elusive until 2020 when cryo-electron microscopy revealed SIgA and SIgM to be remarkably asymmetric antibody assemblies. More recent reports have uncovered IgM and IgA complexes with host receptors and pathogenic virulence factors, species-specific structural differences, and conformational relationships between pIgs' structural cores and antigen binding fragments. Together, these findings highlight pIg and SIg conformational asymmetry as a key feature and establish a foundation to advance our understanding of pIg and SIg structure-function relationships critical for understanding immunity.
Polymeric (p) immunoglobulins (Igs) and their secretory (S) forms are critical to vertebrate immunity. The pIgs and SIgs comprise a molecularly diverse family of antibodies that contain multiple Ig monomers, up to one joining chain (JC), and up to one secretory component. A subset of pIgs function in circulation whereas SIgs populate mucosal barriers. The pIgs and SIgs exhibit unique functions compared to monomeric Igs, yet their underlying molecular structures remained largely elusive until 2020 when cryo-electron microscopy revealed SIgA and SIgM to be remarkably asymmetric antibody assemblies. More recent reports have uncovered IgM and IgA complexes with host receptors and pathogenic virulence factors, species-specific structural differences, and conformational relationships between pIgs' structural cores and antigen binding fragments. Together, these findings highlight pIg and SIg conformational asymmetry as a key feature and establish a foundation to advance our understanding of pIg and SIg structure-function relationships critical for understanding immunity.
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