Enzymatic labeling of a single chain variable fragment of an antibody with alkaline phosphatase by microbial transglutaminase

Functional cross-linking of a single chain Fv fragment of anti-hen egg-white lysozyme antibody (scFv) and alkaline phosphatase (AP) was explored using microbial transglutaminase (MTG) from Streptomyces mobaraensis. A specific peptidyl linker for MTG was genetically fused to the N-terminus of each protein and the resultant proteins were obtained separately by bacterial expression. The recombinant peptide-tagged scFv and AP were site-specifically cross-linked by MTG through the extra peptidyl linkers in vitro, which mainly yielded the heterodimer (i.e., scFv-AP conjugate). The enzymatic cross-linking reaction had little influence on either the antigen-binding ability of the scFv moiety or the enzymatic activity of the AP moiety of the conjugate, allowing use within an enzyme-linked immunosorbent assay. The results obtained suggest that the enzymatic approach with MTG facilitates the posttranslational construction of functional fusion proteins.