Method of crosslinking two objects of interest

The invention provides a method of crosslinking two objects of interest, comprising the steps of : i) providing a fusion protein comprising at least a first protein and a second protein, wherein both the first and the second protein are, based on their structure and function, capable of forming a covalent bond with given substrates, and which first and second proteins are of substantially non-overlapping substrate selectivity, preferably of different substrate specificity ii) providing a first object of interest, comprising a substrate moiety for the first protein of the said fusion protein, and providing a second object of interest, comprising a substrate moiety for the second protein of the said fusion protein and iii) reacting said first protein of the fusion protein with the substrate moiety of said first object, and reacting said second protein of the fusion protein with the substrate moiety of said second object, thereby covalently crosslinking the first object to the second object via the said fusion protein. Most prominent applications of the disclosed method are, due to the straight-forward, reliable, directional and fast crosslinking reactions: the derivatization of cells, antibodies and the crosslinking of proteins.