| The bacterial genome exhibits notable plasticity but is relatively static when compared to the proteome. Protein expression can vary significantly depending on environmental factors, growth stage or stochastic processes within cells. This highly variable character, coupled with the large dynamic range of protein expression levels and the complexity achieved through processes such as post-translational modification (PTM), necessitate accurate, sensitive and high-throughput methods of analysis. The primary aim of this research was to develop an integrated experimental and analysis workflow that combines the analytical power of top-down and bottom-up mass spectrometry towards protein isoform and PTM characterization. We apply this approach to a comprehensive characterization of Escherichia coli ribosomal protein isoform heterogeneity. Our findings uncovered a significant level of heterogeneity in the posttranslational modification of a number of ribosomal proteins, revealing a possible mechanism for the regulation of ribosomal protein function both within and beyond the ribosome. |
