Date of Award

Spring 6-7-2020

Document Type

Honors Project

University Scholars Director

Dr. Christine Chaney

First Advisor/Committee Member

Dr. Benjamin McFarland

Second Advisor/Committee Member

Dr. Jennifer Tenlen

Keywords

mycoplasma genitalium, m. genitalium, SPR, antibody, kinetics, recombinant proteins

Abstract

Mycoplasma genitalium is a sexually-transmitted bacterial pathogen that persists in patients by adherence to cells through 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 values of binding events. Binding of polyclonal rabbit antibodies (3935 and 3936) raised against MgpB-4a was measured against recombinant protein fragments truncated at the N- and C-termini. The two antibody sera produced by two separate, identical inoculations exhibit different kinetics and thermodynamics of binding while binding tightly and specifically to fragments of the mycoplasma adhesin domain MgpB-4a. Antibodies from both rabbits bound tightly to MgpB-4a fragments with dissociation constants of 10 nM-1 pM. A higher temperature (37°C) reduced binding of fragments to both antibodies, affecting 3936 more than 3935. Each antibody exhibits different kinetic signatures, with 3935 binding more tightly to smaller protein fragments and 3936 binding more tightly to larger fragments. Both antibodies bind tightly and with similar dissociation rates too slow to measure, differing most in on-rates. The 3935 and 3936 antibodies are specific to the MgpB-4a domain, as other antibodies raised against MgpB-B bind to the same fragments at higher dissociation constants of 1 μM. Future experiments will compare these binding signatures to those of patient antibodies to explain how antibodies are avoided in vivo.

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