Site-specific modification of proteins with microbial transglutaminase (MTG) is a powerful and versatile strategy for a controlled modification of proteins under physiological conditions. We present evidence that solid-phase microbead-immobilization can be used to site-specifically and efficiently attach different functional molecules important for further downstream applications to proteins of therapeutic relevance including scFV, Fab-fragment and antibodies. We demonstrate that MTG remained firmly immobilized with no detectable column bleeding and that enzyme activity was sustained during continuous operation, which allowed for a convenient recycling of the enzyme, thus going beyond solution-phase MTG conjugation. In addition it is showed that immobilized MTG shows enhanced selectivity towards a certain residue in the presence of several reactive residues which are all targeted if the conjugation was carried out in solution.
