Mycoplasma genitalium is a sexually-transmitted bacterial pathogen that persists in patients by adherence to cells and matrix glycoproteins and evasion of host antibodies. The MgpB and MgpC adherence proteins consist of variable and conserved regions. Variable regions undergo antigenic variation to avoid specific antibodies, however, the C-terminus (MgpB-4a) does not vary, is highly immunogenic, and antibodies to this region inhibit attachment and promote bacterial killing in vitro. To better understand how M. genitalium avoids clearance by antibodies to MgpB-4a in vivo we used surface plasmon resonance (SPR) to measure kinetic and thermodynamic values of binding events between recombinant 4a fragments and mutants and antibodies from rabbits immunized with 4a. We determined binding kinetics between immobilized 4a domain fragments truncated at the N- and C-termini and polyclonal anti-MgpB-4a antibodies produced in two rabbits (3935 and 3936). Antibodies from both rabbits bound tightly to MgpB-4a fragments with dissociation constants of 10 nM-1 pM, binding most tightly to the C-terminal fragment of MgpB-4a at 25°C. Binding was specific, because antibodies from rabbits immunized with a different domain of MgpB did not bind any MgpB-4a fragments significantly. A higher temperature (37°C) reduced binding of fragments to both antibodies, affecting 3936 antibodies more than 3935. Antibodies from each rabbit exhibited different kinetic signatures of binding, with 3935 binding more tightly to smaller protein fragments and 3936 binding more tightly to larger fragments. N and C terminal deletions affected the on-rates of antibody binding but off-rates remained constant within the limit of SPR detection. Future experiments will compare these binding signatures to those of patient antibodies to explain how antibodies are avoided in vivo. Antibodies produced in two rabbits both bind tightly and specifically to fragments of the mycoplasma adhesin domain MgpB-4a, while exhibiting different kinetics and thermodynamics of binding.

Epitope mapping and the kinetic signatures of antibody binding to the Mycoplasma genitalium MgpB adhesin protein

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.