Characterization and Metabolic Function of a Peroxisomal Sarcosine and Pipecolate Oxidase from Arabidopsis

Abstract

Sarcosine oxidase (SOX) is known as a peroxisomal enzyme in mammals and as a sarcosine-inducible enzyme in soil bacteria. Its presence in plants was unsuspected until the Arabidopsis genome was found to encode a protein (AtSOX) with ϳ33% sequence identity to mammalian and bacterial SOXs. When overexpressed in Escherichia coli, AtSOX enhanced growth on sarcosine as sole nitrogen source, showing that it has SOX activity in vivo, and the recombinant protein catalyzed the oxidation of sarcosine to glycine, formaldehyde, and H 2 O 2 in vitro. AtSOX also attacked other N-methyl amino acids and, like mammalian SOXs, catalyzed the oxidation of L-pipecolate to ⌬ 1 -piperideine-6-carboxylate. Like bacterial monomeric SOXs, AtSOX was active as a monomer, contained FAD covalently bound to a cysteine residue near the C terminus, and was not stimulated by tetrahydrofolate. Although AtSOX lacks a typical peroxisome-targeting signal, in vitro assays established that it is imported into peroxisomes. Quantitation of mRNA showed that AtSOX is expressed at a low level throughout the plant and is not sarcosine-inducible. Consistent with a low level of AtSOX expression, Arabidopsis plantlets slowly metabolized supplied [ 14 C]sarcosine to glycine and serine. Gas chromatography-mass spectrometry analysis revealed low levels of pipecolate but almost no sarcosine in wild type Arabidopsis and showed that pipecolate but not sarcosine accumulated 6-fold when AtSOX expression was suppressed by RNA interference. Moreover, the pipecolate catabolite ␣-aminoadipate decreased 30-fold in RNA interference plants. These data indicate that pipecolate is the endogenous substrate for SOX in plants and that plants can utilize exogenous sarcosine opportunistically, sarcosine being a common soil metabolite.

Integrative Modeling of Oxidative Stress and C1 Metabolism Reveals Upregulation of Formaldehyde and Downregulation of Glutathione

“…This is likely due to the fact that, in the C1 metabolism model, not only are the effects on the formaldehyde detoxification being considered, but also its coupled effects with methionine biosynthesis and the activated methyl cycle. The activated methyl cycle contributes to formaldehyde production from sarcosine [18]. In summary, oxidative stress affects C1 metabolism by not only increasing the rate and quantity of formaldehyde concentrations through the activated methyl cycle, for example, but also by reducing the rate and quantity of formaldehyde clearance in the formaldehyde detoxification pathway.…”

Pipecolic acid enhances resistance to bacterial infection and primes salicylic acid and nicotine accumulation in tobacco

“…Arabidopsis contains pipecolate oxidase (PIPOX) that catalyzes the conversion of Pip to δ 1 -piperideine-6-carboxylic acid, a precursor of Aad. 47 Direct catabolism of Pip to Aad might contribute to modulating the levels of Pip in different physiological situations. Microarray data show that the Arabidopsis PIPOX gene is downregulated in leaves upon P. syringae-inoculation (https://www.genevestigator.com/ gv), consistent with attenuated conversion of Pip to Aad in defense situations when the accumulation of the Pip signal is necessary.…”

Stitching together the Multiple Dimensions of Autophagy Using Metabolomics and Transcriptomics Reveals Impacts on Metabolism, Development, and Plant Responses to the Environment inArabidopsis

“…2-Hydroxyglutarate is known to participate in butanoate metabolism and is involved in lysine and aromatic amino acid catabolic pathways that can be used under certain circumstances to support mitochondrial respiration (Engqvist et al, 2011). 2-Aminoadipate is also involved in the lysine degradation pathway as a pipecolate catabolite (Goyer et al, 2004). Interestingly, pipecolate also accumulated in the mutant/RNAi lines, but only under low nitrate supply.…”