Back to the future--the value of single protein species investigations

In proteomics, in the past years, there was a focus on high throughput and reaching of large numbers of identified proteins with the basic discourse of protein expression. To avoid the impression of producing pure lists attempts are usually made to correlate proteins changed in amount between two biological situations to different pathways or protein interactions. This discourse is based on two simplifications, which limit the applicability of proteomics drastically: (i) it is sufficient to quantify a protein from several enzymatic digestion products; (ii) a biological situation is sufficiently described, if a peptide with its PTM is identified, resulting in long lists of modified peptides with data amounts, which are not anymore made accessible for the reader of a publication. The elucidation of N-terminal methylation of proteasome subunit Rpt1 in yeast by Kimura et al. (Proteomics 2013, 13, 3167-3174), which represents the focus on one protein, shows the value of solid chemical analysis with a complete data documentation and paves the way to proteomics based on the protein speciation discourse.