Purification of recombinant proteins remains a critical challenge for applications ranging from basic biological research to the development and production of lifesaving biopharmaceuticals. At laboratory scales, the rapid purification of large numbers of new and uncharacterized protein targets effectively compels the use of affinity tags, which enable reliable purification using simple, established protocols with minimal optimization. Tags cannot be used for therapeutic applications, however, because of their potential for immunogenicity. Thus, for proteins other than monoclonal antibodies (which typically use…