Solid-phase capture for the detection and relative quantification of S-nitrosoproteins by mass spectrometry

Abstract

The proteomic analysis of S-nitrosylated protein (SNO-proteins) has long depended on the biotin switch technique (BST), which requires blocking of free thiols, ascorbate-based denitrosylation of SNO-Cys, biotinylation of nascent thiol and avidin-based affinity isolation. A more recent development is resin assisted-capture of SNO-proteins (SNO-RAC), which substitutes thiopropyl Sepharose (TPS) for biotin-avidin, thus reducing the number of steps required for enrichment of S-nitrosylated proteins. In addition, SNO-RAC facilitates on-resin proteolytic digestion following SNO-protein capture, greatly simplifying the purification of peptides containing sites of S-nitrosylation ("SNO-sites"). This resin-based approach has also now been applied to detection of alternative Cys-based modifications, including S-palmitoylation (Acyl-RAC) and S-oxidation (Ox-RAC). Here, we review the important steps to minimize false-positive identification of SNO-proteins, give detailed methods for processing of protein-bound TPS for mass spectrometry (MS) based analysis, and discuss the various quantitative MS methods that are compatible with SNO-RAC. We also discuss strategies to overcome the current limitations surrounding MS-based SNO-site localization in peptides containing more than one potential target Cys residue. This article therefore serves as a starting point and guide for the MS-focused exploration of SNO-proteomes by SNO-RAC.

Keywords: CysNO; GSNO; LC-MS/MS; Mass spectrometry; Nitric oxide; Nitrosative; Palmitoylation; Proteomics; Redox; S-nitrosocysteine; S-nitrosoglutathione; S-nitrosothiol; S-nitrosylation; SILAC; SNO; SNO-RAC; TMT; iTRAQ; isobaric tags for relative and absolute quantitation; liquid chromatography tandem mass spectrometry; resin-assisted capture of S-nitrosothiols; stable isotope labeling of amino acids in culture; tandem mass tag.