Affinity purification, combined with mass spectrometry (AP-MS) is considered a pivotal technique in protein-protein interaction studies enabling systematic detection at near physiological conditions. The addition of a quantitative proteomic method, like SILAC metabolic labeling, allows the elimination of non-specifically bound contaminants which greatly increases the confidence of the identified interaction partners. Compared to eukaryotic cells, the SILAC labeling of bacteria has specificities that must be considered. The protocol presented here describes the labeling of bacterial cultures with stable isotope-labeled amino acids, purification of an affinity-tagged protein, and sample preparation for MS measurement. Finally, we discuss the analysis and interpretation of MS data to identify and select the specific partners interacting with the protein of interest. As an example, this workflow is applied to the discovery of potential interaction partners of glyceraldehyde-3-phosphate dehydrogenase in the gram-negative bacterium Francisella tularensis.

University of Defence Faculty of Military Health Sciences Department of Molecular Pathology and Biology Hradec Kralove Czech Republic

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