Novel approach for labeling of biopolymers with DOTA complexes using in situ click chemistry for quantification

In this work, we present a two-step labeling approach for the efficient tagging with lanthanide-containing complexes. For this purpose, derivatization of the cysteine residues with an alkyne group acting as linker was done before the DOTA complex was introduced using in situ click chemistry. The characterization of this new methodology is presented including the optimization of the labeling process, demonstration of the quantitative capabilities using both electrospray ionization mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS) detection, and study of the fragmentation behavior of the labeled peptides by collision-induced dissociation (CID) for identification purposes. The results show that, in terms of labeling efficiency, this new methodology improves previously developed DOTA-based label strategies, such as MeCAT-maleimide (metal-coded affinity tag, MeCAT-Mal) and MeCAT-iodoacetamide (MeCAT-IA) reagents. The goal of reducing the steric hindrance caused by the voluminous DOTA complex was fulfilled allowing both, quantification and identification of labeled biopolymers.