Regulation of plant metabolic function mediated by protein S-nitrosylation

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S-Nitrosylation of cysteine residues is a critical redox modification that regulates a broad spectrum of protein functions, and this process involves reactive nitrogen species (RNS) such as S-nitrosothiols (RSNO) that are known to modify the thiol moiety of proteins. This research attempted to examine: (1) the importance of RSNO metabolism in modulating protein S-nitrosylation in higher plants, with special focus on the regulatory role of S-nitrosoglutathione reductase (GSNOR) as a key enzyme determining cellular RSNO levels and the degree of S-nitrosylation; and (2) the possibility that this posttranslational modification may participate in the regulation of certain plant metabolic functions such as nitrogen assimilation.(1) When exposed to RNS such as NO_2, NO donors and nitrate, Arabidopsis plants increased the level of RSNO, a substantial proportion of which was recovered in high-molecular fractions. This suggests the proteinous nature of accumulated RSNO in response to these inorg … More anic nitrogen oxides. Using biotin-switch method, the changes in S-nitrosylated protein levels were monitored and it was found that NO-donor treatments enhanced protein S-nitrosylation in wild-type plants. Overexpression of GSNOR, however, alleviated the extent of this posttranslational modification, with the increased level much lower than that seen in wild-type plants, supporting the importance of this enzyme in modulating protein S-nitrosylation.(2) The physiological consequence of GSNOR overexpression was investigated with respect to the regulatory aspects of nitrogen assimilation. When fed with a single ^<15>N-labeled nitrogen source such as nitrate or NO_2, transgenic plants overexpressing GSNOR incorporated and assimilated more nitrate-and NO_2-derived ^<15>N than did the wild-type plants. Because GSNOR is catalytically not related to the assimilatory process of inroganic nitrogen, these results suggest the possible involvement of GSNOR, and hence S-nitrosylation of proteins, in the regulation of nitrogen assimilation. Less