The structure, biophysics and bioengineering of secretory immunoglobin A

Secretory (S) Immunoglobulins (Igs) are the predominant class of antibodies that are produced and secreted into the vertebrate mucosa. In the mucosa, SIgs play multiple roles, which includes neutralization of toxins, coating and crosslinking of pathogenic and commensal microbes leading to the clearance of harmful antigens and the establishment of mucosal homeostasis. Until 2020, the molecular structures of SIgs remained unreported, masking their functional mechanisms, and limiting their development as therapeutics. In humans, SIgs are mainly composed of IgA, accordingly, called Secretory (S) IgA. In SIgA, IgA adopts a polymeric structure that is different from its serum counterpart, which is predominantly monomeric (m) IgA. The formation of SIgA begins in the lamina propria, where plasma cells assemble between two to five copies of mIgA, along with a protein called Joining chain (JC), to form polymeric (p) IgA. The pIgA, predominantly exists in dimeric (d) forms. The dIgA produced by plasma cells then binds the polymeric Immunoglobin Receptor (pIgR), a membrane bound receptor expressed on the basolateral surface of the mucosal epithelial cells, and subsequently gets transcytosed to the mucosa. There, the pIgR ectodomain (a.k.a Secretory Component; SC), which includes five Ig-domain, D1-D5, is cleaved and remains bound to the dIgA. This SC-dIgA complex is called SIgA. My PhD dissertation research aimed to determine the structures and assembly mechanisms of SIgA and use that information to engineer chimeric SIgA-based molecules to investigate SIgA based effector functions and SIgA therapeutic potential. In Chapter-1, I introduce SIgA's role in mucosal immunity as well as antibody engineering approaches and challenges. In Chapter-2, I report Cryo-EM structures of SIgA and dIgA revealing a first glimpse at the most abundant mammalian antibody and the functional significance of its structure. In Chapter-3, I report the biophysical characterization of SIgA assembly mechanisms, offering insights into SC-dIgA binding mechanisms. In Chapter-4, I report structure-based engineering of chimeric SIgAs (cSIgAs), their ability to neutralize Clostridiodes difficile antigens, their ability to serve as toolkit to investigate SIgA functions, and their potential to serve as biologics to treat disease. In the final chapter, Chapter 5, I explore the broader implications of my research on the assembly, structure, and bioengineering of SIgA.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biochemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Kumar Bharathkar, Sonya

Contributors dc:contributor

• Stadtmueller, Beth M
• Nair, Satish K
• Slauch, James M
• Wu, Nicholas C

• Effector Functions
• Antibody Engineering
• Antibody Developability
• Antibody Functions
• Secretory Immunoglobin A
• Siga
• Polymeric Iga
• Piga
• Diga
• Miga
• Iga
• Mucosa
• Secretory Component
• Sc
• Clostridiodes Difficile
• Tcda
• Tcdb
• Cryo-em
• Cryo Electron Microscopy
• Surface Plasmon Resonance
• Spr
• Antibodies
• Neutralization

Statement dc:rights

• Copyright 2023 Sonya Kumar Bharathkar

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122130

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122130