Proteomics based on two-dimensional (2-D) gel electrophoresis of proteins followed by spot identification with mass spectrometry is a commonly used method for physiological studies. Physiological proteomics requires 2-D reference maps, on which most of the main proteins are identified. We present a reference map for the bacterial plant pathogen Agrobacterium tumefaciens proteins, which contains more than 300 entries with an isoelectric point (p/) between 4 and 7. The quantitative study of the proteins in the analytical window of the master gel demonstrated unique features, in comparison with other bacteria. In addition, a theoretical analysis of several protein parameters was performed and compared with the experimental results. A comparison of the theoretical molecular weight (MW) of the proteins and their theoretical p/ with their vertical and horizontal migration distances, respectively, pointed out the existence of several proteins that strongly diverted from the graph trend-line. These proteins were clearly subjected to post-translational modifications, which changed their p/ and/or MW. Additional support for post-translational modifications comes from the identification of multiple spots of the same gene products. Post-translational modifications appear to be more common than expected, at least for soluble proteins, as more than 10% of the proteins were associated with multiple spots.
- Mass spectrometry
- Post-translational modifications
- Stress response