On-Membrane Dynamic Interplay between Anti-GM1 IgG Antibodies and Complement Component C1q

Abstract

Guillain-Barré syndrome, an autoimmune neuropathy characterized by acute limb weakness, is often preceded by Campylobacter jejuni infection. Molecular mimicry exists between the bacterial lipo-oligosaccharide and human ganglioside. Such C. jejuni infection induces production of immunoglobulin G1 (IgG1) autoantibodies against GM1 and causes complement-mediated motor nerve injury. For elucidating the molecular mechanisms linking autoantigen recognition and complement activation, we characterized the dynamic interactions of anti-GM1 IgG autoantibodies on ganglioside-incorporated membranes. Using high-speed atomic force microscopy, we found that the IgG molecules assemble into a hexameric ring structure on the membranes depending on their specific interactions with GM1. Complement component C1q was specifically recruited onto these IgG rings. The ring formation was inhibited by an IgG-binding domain of staphylococcal protein A bound at the cleft between the C H 2 and C H 3 domains. These data indicate that the IgG assembly is mediated through Fc-Fc interactions, which are promoted under on-membrane conditions due to restricted translational diffusion of IgG molecules. Reduction and alkylation of the hinge disulfide impaired IgG ring formation, presumably because of an increase in conformational entropic penalty. Our findings provide mechanistic insights into the molecular processes involved in Guillain-Barré syndrome and, more generally, into antigen-dependent interplay between antibodies and complement components on membranes.

Quantitative Visualization of the Interaction between Complement Component C1 and Immunoglobulin G: The Effect of CH1 Domain Deletion

“…To address this issue, we quantified their IgG-binding affinities using GB2, a mouse monoclonal IgG2b antibody, which is directed against Campylobacter jejuni and cross-reacts with GM1 ganglioside [20]. Our previous HS-AFM study showed that GB2 antibodies assembled into hexameric rings on GM1-containing membranes and thereby recruited C1q [13]. Here, we compared the recruitment extent onto the IgG assemblages on the antigen-incorporated membranes between C1 and C1q.…”

“…Another mechanism is assembling antigen-bound IgG molecules, facilitating their multivalent interactions with effector molecules. Indeed, IgG molecules are self-assembled into a hexameric ring on antigen-containing membranes, recruiting C1q, a subcomponent of the first component of the classical complement pathway [13,14]. Hexamer formation of IgG is mediated through the interfacial region between the CH2 and CH3 domains and can be enhanced by mutational modification at the region, which therefore can be a target for improving complement-dependent cytotoxicity (CDC) of therapeutic antibodies [15,16].…”

“…We have established a method for quantitatively visualizing IgG interactions with C1q and FcγRIII by high-speed atomic force microscopy (HS-AFM) [11,13]. Here we apply this method to characterize the interaction between IgG and the C1 complex, comprising C1q, C1r, and C1s.…”

Biophysical characterization of dynamic structures of immunoglobulin G

“…High-speed atomic force microscopy (HS-AFM) offers a powerful emerging tool for observing dynamic behaviors of IgG. Several studies have been reported real-time observation of the interactions of IgG molecules with antigens and effector molecules on membrane-like surfaces (Yogo et al 2019;Yanaka et al 2019b;Strasser et al 2019).…”

“…Antibodies exert their multiple functions in a highly coordinated manner, as best exemplified by the interlocking of promotion of effector functions with antigen recognition (Yang et al 2017). Recent HS-AFM data illustrate that IgG molecules bound to antigenic membranes are self-assembled into a hexameric ring and thereby recruit C1q (Yanaka et al 2019b;Yogo et al 2019). Moreover, Fab portions of IgG contribute to its interaction with FcγRIII (Yogo et al 2019).…”