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Abstract Detail

Oxidative Stress

Jain, Vanita [1], Qiu, Quan-Sheng [1], Oh, Man-Ho [2], Huber, Steven [3].

Apparent sensitivity of nitrate reductase phosphorylation to oxidative signals.

Phosphorylation of the Ser534 site on Arabidopsis nitrate reductase (NR) is required for binding of a 14-3-3 protein to form an inactive complex. The site conforms to the minimal canonical motif targeted by calcium-dependent protein kinases (CDPKs): Φ-x-[KR]-x-x-[ST]-x-x-x-Φ, where Φ is a hydrophobic amino acid. A synthetic peptide based on the Arabidopsis NR-Ser534 sequence (SLKKSVSTPFMN) is a good substrate for CDPKs in vitro. Interestingly, treatment of the NR-Ser534 peptide with 5% H2O2 to oxidize the Met residue (at the essential pS+4 position) to Met sulfoxide (MetSO), strongly inhibited peptide phosphorylation in vitro. This effect may also occur in vivo, because Arabidopsis plants over expressing PMSRA3, which encodes a cytosolic peptide methionine sulfoxide reductase, had increased apparent phosphorylation stoichiometry of NR relative to wild type plants when leaves were darkened. In illuminated leaves, apparent NR phosphorylation stoichiometries were lower compared to darkened leaves, and similar between the PMSRA3 transgenic and wild type plants. Associated with the increased phosphorylation of NR in the transgenic plants was increased content of NR protein after extended darkness. Collectively the results are consistent with the notion that in darkened leaves, oxidation of Met at the pS+4 position occurs and reduces NR phosphorylation as a result of motif alteration. This reduces formation of the phosphoNR:14-3-3 complex and hence, NR protein is degraded more rapidly in darkened leaves. Efforts are underway to obtain PMSRA3 knock out plants for comparison to the over expressing plants, and to study MetSO reduction in synthetic peptide substrates using recombinant PMSRA3 in vitro to characterize the substrate specificity of this enzyme.

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1 - Univ of Illinois, Plant Biology
2 - USDA-ARS, Univ of Illinois, Plant Biology
3 - USDA-ARS, Univ of Illinois, Plant Biology, 1201 W. Gregory Drive, 197 ERML, Urbana, IL, 61801, USA

methionine sulfoxide
nitrate reductase
14-3-3 protein
methionine sulfoxide reductase
phosphorylation motif.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P06022
Abstract ID:1704

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