For a young person, turning 18 is a big milestone. In most countries, this is the age when you are legally recognized as an adult, able to vote in elections and are eligible for military service. For many, it also is a year filled with major life changes: graduating high school, starting college or entering the workforce full time. For myself, this involved moving cross country, making new friends, and living on my own. Although navigating all these changes in a year can sometimes be overwhelming, overcoming new challenges is fundamental to helping us gain wisdom, experience and maturity.
Life changes, however, are not limited to those experienced by 18-year-olds. For myself, another major change happened early in my career when I joined a new research group. After my company merged to become Thermo Fisher Scientific, my team was tasked with developing new reagents for the quantitative proteomics market. At the time, most research groups were primarily using spectral counting or differential analysis of 2D gel spots to identify protein abundance changes. However, sample labeling using isotopic mass tags (e.g., I-CAT) or amino acids (e.g. SILAC) was quickly gaining traction. These labeling technologies not only provided accurate relative quantitation of protein abundance changes, but also enabled sample multiplexing where more than one sample is combined into a single sample for LC-MS analysis.
Concurrent, quantitative analysis of samples using isotopic labeling was a significant improvement over label-free analysis of individual samples. Yet, these methods resulted in fewer protein identifications due to an increase in sample feature (i.e., MS1) complexity and were limited to analysis of a few samples simultaneously. Fortunately, our team and others helped develop isobaric tags that used tandem mass spectrometry (e.g., TMT and iTRAQ) for quantitation. As these labeling reagents have the same nominal mass, they enable higher sample multiplexing without increasing MS complexity.
Over the last decade, tandem mass tag (TMT) technology has grown to become one of the predominant methods for global protein quantitation. Advancements in isobaric tag reagent chemistry, instrument hardware, acquisition methods, and data analysis software over the years have helped expand the level of proteomic sample multiplexing from six to 16 samples. Recently, a new set of tags were launched to complete the Thermo Scientific™ TMTpro™ isobaric label reagent set that support multiplexing 18 samples in a single LC-MS run. With this new number of samples that can be analyzed together, it looks like proteomics sample multiplexing has truly come of age.