High Performance Liquid Chromatography-Electrospray Ionization Mass Spectrometry (LC-MS) was performed using a Dionex UltiMate® 3000 Ci Rapid Separation LC system equipped with an UltiMate® 3000 photodiode array detector probing at 250-400 nm, coupled to a HCT ultra ETD II (Bruker Daltonics) ion trap spectrometer, using Chromeleon® 6.80 SR12 software (ThermoScientific), esquireControl version 6. Prior to analysis by LC-MS, peptides were diluted 1:3 in water and then further diluted 1:1 in acetonitrile with 1% (v/v) formic acid. Peptide samples were chromatographically analysed using an Ascentis Express C18, 2.7 µm (5 cm x 4.6 mm, Supelco). Water with 0.1% (v/v) formic acid (solvent A) and acetonitrile with 0.1% (v/v) formic acid (solvent B) were used as the mobile phase at a flow rate of 0.3 mL min -1 at RT (RT). A multistep gradient of 9.2 min was programmed as follows: 5% B for 0 min, a linear gradient to 10% B over 1 min, 10% B for 1 min, a linear gradient to 50% B over 2 min, a linear gradient to 90% B over 1 min, 90 % B for 2 min, linear gradient to 5% B over 1 min, 5% B for 1 min. Note that the multistep gradient finishes in 5% B in order to re-equilibrate the column. Under these conditions, all peptides typically eluted between 2 and 7 min.