mTMT: An alternative, non-isobaric, tandem mass tag allowing for precursor-based quantification

Stable isotope labeling of peptides is the basis for numerous mass spectrometry-based quantification strategies. Isobaric tagging and metabolic labeling, namely TMT and SILAC, are among the most widely used techniques for relative protein quantification. Here we report an alternative, precursor-based quantification method using non-isobaric TMT variants: TMT0 (TMTzero) and shTMT (super-heavy TMT). We term this strategy mTMT (mass difference tandem mass tagging), as these TMT variants differ by 11 mass units; yet, peptides labeled with these reagents co-elute, analogous to SILAC-labeled sample analysis. As proof-of-concept, we profiled the proteomes of two cell lines that are frequently used in neuroscience studies, SH-SY5Y and SVGp12, using mTMT and standard SILAC-labeling approaches. We show similar numbers of quantified proteins and peptides using each method with highly correlated fold changes between workflows. We conclude that mTMT is a suitable alternative for precursor-based protein quantification.