Efficient Site‐Specific Antibody–Drug Conjugation by Engineering a Nature‐Derived Recognition Tag for Microbial Transglutaminase

Abstract Microbial transglutaminase (mTG) has recently emerged as a powerful tool for antibody engineering. In nature, it catalyzes the formation of amide bonds between glutamine side chains and primary amines. Being applied to numerous research fields from material sciences to medicine, mTG enables efficient site‐specific conjugation of molecular architectures that possess suitable recognition motifs. In monoclonal antibodies, the lack of native transamidation sites is bypassed by incorporating specific peptide recognition sequences. Herein, we report a rapid and efficient mTG‐catalyzed bioconjugation that relies on a novel recognition motif derived from its native substrate Streptomyces papain inhibitor (SPI P ). Improved reaction kinetics compared to commonly applied sequences were demonstrated for model peptides and for biotinylation of Her2‐targeting antibody trastuzumab variants. Moreover, an antibody–drug conjugate assembled from trastuzumab that was C‐terminally tagged with the novel recognition sequence revealed a higher payload‐antibody ratio than the reference antibody.