Proteomic Mapping of Mitochondria in Living Cells via Spatially Restricted Enzymatic Tagging

Mitochondrial Makeup Mapped Because mass spectrometry (MS) cannot be performed on living cells, biologists currently recover spatial information indirectly, by purifying organelles or protein complexes prior to MS analysis. These purifications often yield false positives because of sample contamination and false negatives because of material loss. Rhee et al. (p. 1328 , published online 31 January) present an approach that bridges microscopy and proteomics to produce a spatially and temporally resolved proteomic map of mitochondria from living cells. A nonspecific labeling enzyme (peroxidase) was genetically targeted to the mitochondria within live cells, where it tagged endogenous proteins in a spatially restricted manner within a 1-minute window, for subsequent identification and analysis by MS. This rapid and straightforward technology provides the ability to access otherwise inaccessible cellular regions and requires a very small amount of starting material.