Scheme 1. Site-specific labeling of IgG antibodies. In a first reaction, N-linked glycans are removed by PNGaseF, and only the available glutamines (Q) at position −2 relative to the deglycosylated sites are modified with H2N-PEG3-N3 catalyzed by microbial transglutaminase (mTG). In a second reaction, fluorophores(-DIBO) or ssDNA(-DBCO) are attached to the azide-modified antibodies using strain-promoted azide–alkyne cycloaddition (SPAAC).
