Publication Date


Document Type


First Advisor

Horn, James J.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Chemistry and Biochemistry


pH dependent protein-protein interactions are of great importance for various biological processes. In addition, the generation of engineered pH-dependent therapeutic antibodies opens opportunities for the extension of therapeutic half-life, thereby reducing drug dosage or frequency of administration, as well as providing pH-dependent targeting, such as the tumor microenvironment. Engineering pH-dependent antibody-antigen interaction is mostly achieved through the incorporation of ionizable residues within the antigen binding interface. These ionizable residues must undergo a change in environment upon forming a protein-protein complex, which causes a change in the ionizable group’s pKa value. This coupled protonation equilibria is responsible for the observed pH-dependent protein interaction. Most engineered pH-dependent proteins have relied on the introduction of histidine mutagenesis, which resulted in the antibody binding antigen strongly at neutral pH and weakly in acidic pH. Another opportunity in developing pH-dependent proteins involves modifying where the pH switch occurs. Specifically, this is controlled by the environment and its influence of the histidine group’s pKa. Here, two different electrostatic scenarios for a histidine residue within the antigen binding interface of an anti-RNase A VHH were characterized. The influence of repulsive charges on the pH switch point was explored for a double histidine variant of anti-RNase VHH using isothermal titration calorimetry. In addition, the influence of complimentary charges on the pH switch point was explored using an aspartic acid/histidine pair variant of anti-RNase A VHH.


96 pages




Northern Illinois University

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