Engineering pH-Sensitive Single-Domain Antibodies

There is increasing interest in expanding an antibody beyond high affinity and specificity. One such feature is custom regulation of the binding event, such as pH-dependent control. Here, we provide a methodology for generating single-domain antibodies (sdAbs) that bind their antigen in a pH-dependent fashion. As each sdAb is unique, we start by providing the conceptual framework for designing a combinatorial histidine scanning library within a sdAb-antigen-binding interface. Methods are provided to create a phage display library, containing up to 1 × 10¹⁰ unique members where each permutation of histidine substitution is sampled within the confines of the specified interface region(s). Finally, we describe phage display protocols for the selection and analysis of unique pH-dependent sdAb clones.