Method finds fresh proteins

The proteome of cells, tissues, or organisms is always in flux, with new proteins being synthesized and old ones being degraded. A new method could help researchers distinguish the new proteins from those that were already there, leading to a dynamic picture of the proteome. Caltech biologist Erin M. Schuman, chemical engineer David A. Tirrell, and coworkers tag proteins during protein synthesis by replacing methionine with azidohomoalanine (Proc. Natl. Acad. Sci. USA 2006, 103, 9482). The azide group is then labeled with an alkyne affinity handle that can be used to pull the freshly synthesized proteins out of the mix of older proteins. Combining the method with multidimensional liquid chromatography and tandem mass spectrometry, they purified and identified 195 proteins synthesized within a two-hour window.