PMID: 32398862

Authors:

Wang Y, Wang G, Li Y, Zhu Q, Shen H, Gao N, Xiao J

Title:

Structural insights into secretory immunoglobulin A and its interaction with a pneumococcal adhesin.

Journal:

Cell Res. 2020 May 12. pii: 10.1038/s41422-020-0336-3. doi:, 10.1038/s41422-020-0336-3.

Abstract:

Secretory Immunoglobulin A (SIgA) is the most abundant antibody at the mucosal surface. It possesses two additional subunits besides IgA: the joining chain (J-chain) and secretory component (SC). SC is the ectodomain of the polymeric immunoglobulin receptor (pIgR), which functions to transport IgA to the mucosa. How the J-chain and pIgR/SC facilitate the assembly and secretion of SIgA remains incompletely understood. Furthermore, during the infection of Streptococcus pneumoniae, the pneumococcal adhesin SpsA hijacks pIgR/SC and SIgA to gain entry to human cells and evade host defense. How SpsA targets pIgR/SC and SIgA also remains elusive. Here we report a cryo-electron microscopy structure of the Fc region of IgA1 (Fcalpha) in complex with the J-chain and SC (Fcalpha-J-SC), which reveals the organization principle of SIgA. We also present a structure of Fcalpha-J-SC complexed with SpsA, which uncovers the specific interactions between SpsA and human pIgR/SC. These results advance the molecular understanding of SIgA and shed light on S. pneumoniae pathogenesis.