Functional Testing and Localization of Tyrosine Sulfation in a Trispecific Antibody.

Mass spectrometry (MS) is a tool of choice for the in-depth characterization of new biotherapeutic molecules such as a complex naturally derived trispecific antibody (tsAb) that presents a tyrosine sulfation within the variable domain. Although tyrosine sulfation is an important post-translational modification responsible for strengthening protein-protein interactions, its localization is challenging, as the sulfate group is very labile using conventional positive ion mode fragmentation techniques. In this work, we describe the combination of functional testing and MS-based methods to study the impact of tyrosine sulfation in the tsAb. The presence of sulfation was confirmed by intact mass and peptide mapping analyses. For unambiguous localization of the sulfate group, electron activated dissociation (EAD) MS/MS experiments were employed to generate diagnostic fragments carrying an intact sulfate group. We also demonstrated that a significant decrease in binding of the tsAb to the target antigen was observed following the sulfatase treatment. Taken together, the results from this study support the notion that tyrosine sulfation plays an important role in protein-protein interactions.