Structural and functional characteristics of cGMP-dependent methionine oxidation in Arabidopsis thaliana proteins
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Structural and functional characteristics of cGMPdependent methionine oxidation in Arabidopsis thaliana proteins Claudius Marondedze1, Ilona Turek1, Brian Parrott1, Ludivine Thomas1, Boris Jankovic2, Kathryn S Lilley3 and Chris Gehring1*
Abstract Background: Increasing structural and biochemical evidence suggests that post-translational methionine oxidation of proteins is not just a result of cellular damage but may provide the cell with information on the cellular oxidative status. In addition, oxidation of methionine residues in key regulatory proteins, such as calmodulin, does influence cellular homeostasis. Previous findings also indicate that oxidation of methionine residues in signaling molecules may have a role in stress responses since these specific structural modifications can in turn change biological activities of proteins. Findings: Here we use tandem mass spectrometry-based proteomics to show that treatment of Arabidopsis thaliana cells with a non-oxidative signaling molecule, the cell-permeant second messenger analogue, 8-bromo-3,5-cyclic guanosine monophosphate (8-Br-cGMP), results in a time-dependent increase in the content of oxidised methionine residues. Interestingly, the group of proteins affected by cGMP-dependent methionine oxidation is functionally enriched for stress response proteins. Furthermore, we also noted distinct signatures in the frequency of amino acids flanking oxidised and un-oxidised methionine residues on both the C- and N-terminus. Conclusions: Given both a structural and functional bias in methionine oxidation events in response to a signaling molecule, we propose that these are indicative of a specific role of such post-translational modifications in the direct or indirect regulation of cellular responses. The mechanisms that determine the specificity of the modifications remain to be elucidated. Keywords: Methionine oxidation, Reactive oxygen species, 3,5-cyclic guanosine monophosphate, Tandem mass spectrometry-based proteomics, Arabidopsis thaliana
Findings The debate of whether methionine (Met) oxidation of proteins is a purely chemical consequence of cellular oxidative damage or a protective mechanism against oxidative damage, or indeed a post-translational modification that can act as a specific cellular signal and/or response, is ongoing [1-3]. To shed light on this question we treated Arabidopsis suspension culture cells with the cell permeant second messenger analogue 8-bromo 3,5cyclic guanosine monophosphate (8-Br-cGMP). Cyclic * Correspondence: [email protected] 1 Division of Chemical and Life Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Full list of author information is available at the end of the article
GMP has a signaling role in many plant responses, including responses to light [4], hormones [5-8], signaling peptides [9], salt and drought stress [10,11], ozone, and defence responses [12-14]. Given that cGMP is not an oxidising agent and does not induc
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