Size-Sorting Combined with Improved Nanocapillary Liquid Chromatography−Mass Spectrometry for Identification of Intact Proteins up to 80 kDa

Despite the availability of ultra-high-resolution mass spectrometers, methods for separation and detection of intact proteins for proteome-scale analyses are still in a developmental phase. Here we report robust protocols for online LC-MS to drive high-throughput top-down proteomics in a fashion similar to that of bottom-up proteomics. Comparative work on protein standards showed that a polymeric stationary phase led to superior sensitivity over a silica-based medium in reversed-phase nanocapillary LC, with detection of proteins >50 kDa routinely accomplished in the linear ion trap of a hybrid Fourier transform mass spectrometer. Protein identification was enabled by nozzle-skimmer dissociation and detection of fragment ions with <10 ppm mass accuracy for highly specific database searching using tailored software. This overall approach led to identification of proteins up to 80 kDa, with 10-60 proteins identified in single LC-MS runs of samples from yeast and human cell lines prefractionated by their molecular mass using a gel-based sieving system.