Proteomic analysis of S-nitrosylated proteins in potato plant

Nitric oxide (NO) has various functions in physiological responses in plants, such as development, hormone signaling and defense. The mechanism of how NO regulates physiological responses has not been well understood. Protein S-nitrosylation, a redox-related modification of cysteine thiol by NO, is known to be one of the important post-translational modifications to regulate activity and interactions of proteins. To elucidate NO function in plants, proteomic analysis of S-nitrosylated proteins in potato (Solanum tuberosum) was performed. Detection and functional analysis of internal S-nitrosylated proteins is technically demanding because of the instability and reversibility of the protein S-nitrosylation. By using a modified biotin switch assay optimized for potato tissues, and nano liquid chromatography combined with mass spectrometry, approximately 80 S-nitrosylated candidate proteins were identified in S-nitrosoglutathione-treated potato leaves and tuber extracts. Identified proteins included redox-related enzymes, defense-related proteins and metabolic enzymes. Some of identified proteins were synthesized in Escherichia coli, and S-nitrosylation of recombinant proteins was confirmed in vitro. Dehydroascorbate reductase 1 (DHAR1, EC 1.8.5.1), one of the identified S-nitrosylated target proteins, showed glutathione-dependent dehydroascorbate-reducing activity. Either point mutation in a target cysteine of S-nitrosylation or treatment with an NO donor, S-nitroso-L-cysteine, significantly reduced the activity of DHAR1, indicating that DHAR1 is negatively regulated by S-nitrosylation of the cysteine residue essential for the enzymatic activity. These results show that the modified method developed in this study can be used to identify proteins regulated by S-nitrosylation in potato tissues.