To conclude, the ability of bTG enzyme to crosslink BSA was confirmed and peptide mapping experiments were carried out to determine the ligation site. Surprisingly, the identified site for the conjugation was found on an asparagine residue instead of the expected glutamine residue and did not match the recognition sequence reported in the literature. The insertion of this sequence on a non-reactive monobody sequence led to the conjugation of dansylcadaverine and other various primary amines in very good yields (>90%). Increasing the number of amine equivalents did not lead to a higher number of conjugates (data not shown), confirming that the bioconjugation reaction depends on the protein sequence. A deep investigation of the amino acids that are essential for the bioconjugation was performed and the recognition sequence could be reduced to the three amino acids "ENL" and the ten amino acids "DAIPENLPPL" sequences. However, the sequence itself is not the only requirement for the bioconjugation to be possible as it also depends on the accessibility of the reactive amino acids. Therefore, the insertion of the recognition sequence into a protein should be made with careful inspection of the structure of the protein of interest or with the addition of a longer sequence. Several small molecules could be attached to a monobody containing the sequence of interest in good yields, including an siRNA molecule. Conjugation of a small molecule and siRNA on different VHH could also be achieved and brought a better understanding of the sequence requirements, as a few amino acids are needed after the reaction "ENL" for a successful conjugation. A reduced conversion was achieved when IgG was used as a substrate, and a DAR 2 could be obtained on the light chains of the antibody, both with dansylcadaverine and siRNA. These results appear as a promising proof of concept for the more complex conjugation of antibodies and a good starting point for further enzyme evolution. The engineering of the antibody constant domain with an accessible conjugation site is also under consideration.