Operation of the LPI™ FlowCells – multi-step digestion

with PPS Silent® Surfactant PPS Silent® Surfactant (Protein Discovery) is a mass spectrometry compatible reagent designed for the extraction and solubilisation and improvement of in-solution enzymatic protein digestions of hydrophobic proteins. For the first digestion step with trypsin, the same procedure was followed as for the multi-step digestion method without PPS Silent® Surfactant as described above. For the second digestion step, trypsin was resuspended in 20 mM NH4HCO3 pH 8.0 to a final concentration of 5 μg ml-1. The resuspended trypsin was then used to resuspend PPS Silent® Surfactant to a final concentration of 0.1% (w/v). 700 μl of the trypsin containing PPS Silent® Surfactant was then injected

into the LPI™ FlowCell and then incubated at 37°C for 1 h. Captisol The tryptic peptides were collected by injecting 700 μl 20 mM NH4HCO3, pH 8 at the inlet port and collecting the eluant at the outlet port. Formic acid was added to the eluted peptides to a final concentration of 250 mM and incubated for 1 h at room temperature to inactivate the trypsin and cleave the PPS Silent® Surfactant from the sample. The sample was stored at -80°C for further analysis (see Additional File 3). Peptide analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) The peptide fraction collected check details from LPI™ FlowCell was subsequently analyzed separately by LC- MS/MS at the Proteomics Core Facility at the University of Gothenburg. Prior to analysis, the sample was centrifuged in vacuum to dryness and reconstituted in 20 μl 0.1% (v/v) formic acid in water. The sample was centrifuged at 13 000 g for 15 minutes and 17 μl was transferred to the autosampler of the LC-MS/MS system. For the liquid chromatography, an Agilent 1100 binary pump was used and the tryptic peptides were separated on a 200 × 0.05 mm i.d. fused silica column

packed in-house with 3 μm ReproSil-Pur C18-AQ particles (Dr. Maisch, GmbH, Ammerbuch, Germany). Two μl of the sample was RG7420 concentration injected and the peptides were first trapped on a precolumn (45 × 0.1 mm i.d.) packed with 3 μm C18-bonded particles. A 40 minute gradient of 10-50% (v/v) acetonitrile Tau-protein kinase in 0.2% (v/v) formic acid was used for separation of the peptides. The flow through the column was reduced by a split to approximately 100 nl min-1. Mass analyses were performed in a 7-Tesla LTQ-FT mass spectrometer (Hybrid Linear Trap Quadrupole – Fourier Transform; Thermo Electron) equipped with a nanospray source modified in-house. The instrument was operated in the data-dependent mode to automatically switch between MS and MS/MS acquisition. MS spectra were acquired in the FT-ICR while MS/MS spectra were acquired in the LTQ-trap. For each scan of FT-ICR, the six most intense, double- or triple protonated ions were sequentially fragmented in the linear trap by collision induced dissociation (CID). Already fragmented target ions were excluded for MS/MS analysis for 6 seconds.