Assessment of sample preparation bias in mass spectrometry-based proteomics

For mass spectrometry-based proteomics, the selected sample preparation strategy is a key determinant for information that will be obtained. However, the corresponding selection is often not based on a fit-for-purpose evaluation. Here we report a comparison of in-gel (IGD), in-solution (ISD), on-filter (OFD), and on-pellet digestion (OPD) workflows on the basis of targeted (QconCAT-multiple reaction monitoring (MRM) method for mitochondrial proteins) and discovery proteomics (data dependent acquisition, DDA) analyses using three different human head and neck tissues (i.e. nasal polyps, parotid gland, and palatine tonsils). Our study reveals differences between the sample preparation methods, for example with respect to protein and peptide losses, quantification variability, protocol-induced methionine oxidation and asparagine/glutamine deamidation as well as identification of cysteine containing peptides. Moreover, none of the methods performed best for all types of tissues, which seemingly argues against the existence of a universal sample preparation method for proteome analysis.