Project description:Proteome quantification using TMT reagents and off-line basic peptide fractionation was done as described previously in Grand, 2021, with the exception that the isolated nuclei were used as a starting material rather than whole cells to enable detection of transcription factors which are generally less abundant proteins in the cell, and that nine channels from a TMTpro16 reagent kit were used. Briefly, mESCs, NGN2 24h induced cells and MyoD1 24h induced cells were harvested in triplicates of 10 million per sample. Nuclei were isolated by suspending in 4 ml of nuclear extraction buffer (10 mM HEPES pH 7.9, 10 mM KCl, 10 mM EDTA, 0.5% NP-40, 1 mM DTT and complete protease inhibitor (Roche)) and incubating on ice for 10 min with vortexing every 2 minutes. Nuclei were collected by centrifugation (800g, 10 min, 4 °C), washed with ice cold PBS and suspended in 1% sodium deoxycholate in 50 mM HEPES buffer (pH 8.5). The nuclear lysate was disrupted with sonication. Proteins were reduced, alkylated and Lys-C/trypsin digested. Fifty micrograms of peptides from each biological replicate were labelled using channels 128C-131C from a TMT 16plex isobaric labelling reagents kit (Lot# VJ313476, Thermo Fisher Scientific). Dried TMT-labeled peptides were dissolved in 20 μL of 10 mM ammonium formate (pH 10, high pH Buffer A), and high-pH reversed-phase chromatography was employed using an Agilent 1100 HPLC system with an autosampler, a YMC Triart C18 0.5 x 250 mm column, and a fraction collector. The peptides were separated using the following binary buffer system: high-pH Buffer A (20 mM ammonium formate in water, pH 10) and high-pH Buffer B (20 mM ammonium formate pH 10 in 90% acetonitrile) at a flow rate of 12 μL/minute. The gradient duration was a total of 115 min, with mobile phase compositions in %B as follows: 0-5 min at 2%-15%, 5-15 min at 15%-25%, 15-80 min at 25%-45%, 80-85 min at 45%-65%, 85-95 min at 65%-100%, 95-100 min at 100%, 100-101 min at 100%-2%, and 101-115 min at 2%, resulting in 48 fractions after sample concatenation. Samples were acidified with 1% TFA and dried in a speed vac. Peptides reconstituted in 2% acetonitrile, 0.1% formic acid were on-line separated on a C18 50 cm μPAC column using a EASYnLC-1000 system (all Thermo Fisher Scientific) mounted on a Digital PicoView nanospray source (New Objective), connected to an Orbitrap Fusion Lumos mass spectrometer (Thermo Fisher Scientific). Peptide elution was achieved using a linear gradient of increasing concentration of acetonitrile in 0.1% formic acid at a flow rate of 500 nl/min: 0-2 min: 2%, 2-8 min: 2-6%, 8-89 min 6-22%, 89-107 min: 22-40%, 107-111 min: 40-80%, 111-115 min: 80% (washing), 115-116 min: 80-2%, 116-120 min: 2% (equilibration). For MS data acquisition in a data-dependent mode, ions for survey MS1 scans were recorded in profile mode in the Orbitrap detector at a resolution of 120,000 in the range of 400-1400 m/z every 3 seconds for a maximum of 100 ms to reach the normalized AGC target of 50%. The most abundant precursors were selected in the quadrupole within an isolation window of 0.7 m/z for MS2 HCD fragmentation based on advanced peak determination, monoisotopic peak determination set to peptides, within charge states 2-8, dynamic exclusion of 60 s within +/-10 ppm tolerance for isotopes and different charge states, with a minimum intensity of 5e4, with normalized collision energy 34% for a maximum injection time of 200 ms to reach the normalized AGC target of 80%. MS2 HCD spectra were and recorded in the “normal” range, starting at 100 m/z at 50,000 resolution in the Orbitrap analyzer in centroid mode.
2025-08-21 | PXD054143 | Pride