PT  - JOURNAL ARTICLE
AU  - Sonya Kumar Bharathkar
AU  - Benjamin W. Parker
AU  - Andrey G. Malyutin
AU  - Nandan Haloi
AU  - Kathryn E. Huey-Tubman
AU  - Emad Tajkhorshid
AU  - Beth M. Stadtmueller
TI  - The Structures of Secretory and Dimeric Immunoglobulin A
AID  - 10.1101/2020.02.16.951780
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.02.16.951780
4099  - http://biorxiv.org/content/early/2020/10/15/2020.02.16.951780.short
4100  - http://biorxiv.org/content/early/2020/10/15/2020.02.16.951780.full
AB  - Secretory (S) Immunoglobulin (I) A is the predominant mucosal antibody, which binds pathogens and commensal microbes. SIgA is a polymeric antibody, typically containing two copies of IgA that assemble with one joining-chain (JC) to form dimeric (d) IgA that is bound by the polymeric Ig-receptor ectodomain, called secretory component (SC). Here we report the cryo-electron microscopy structures of murine SIgA and dIgA. Structures reveal two IgAs conjoined through four heavy-chain tailpieces and the JC that together form a β-sandwich-like fold. The two IgAs are bent and tilted with respect to each other, forming distinct concave and convex surfaces. In SIgA, SC is bound to one face, asymmetrically contacting both IgAs and JC. The bent and tilted arrangement of complex components limits the possible positions of both sets of antigen binding fragments (Fabs) and preserves steric accessibility to receptor binding sites, likely influencing antigen binding and effector functions.Competing Interest StatementThe authors have declared no competing interest.