Tandem mass spectra were extracted, charge state deconvoluted and deisotoped by [unknown] version [unknown]. All MS/MS samples were analyzed using Sequest (XCorr Only) (Thermo Fisher Scientific, San Jose, CA, USA; version IseNode in Proteome Discoverer 2.2.0.388). Sequest (XCorr Only) was set up to search uniprot-sp_20170328.fasta (unknown version, 505583 entries) assuming the digestion enzyme trypsin. Sequest (XCorr Only) was searched with a fragment ion mass tolerance of 0.60 Da and a parent ion tolerance of 10.0 PPM. Carbamidomethyl of cysteine was specified in Sequest (XCorr Only) as a fixed modification. Oxidation of methionine and acetyl of the n-terminus were specified in Sequest (XCorr Only) as variable modifications.