Catalytic profile of Arabidopsis peroxidases, AtPrx-2, 25 and 71, contributing to stem lignification

PLoS One. 2014 Aug 19;9(8):e105332. doi: 10.1371/journal.pone.0105332. eCollection 2014.

Abstract

Lignins are aromatic heteropolymers that arise from oxidative coupling of lignin precursors, including lignin monomers (p-coumaryl, coniferyl, and sinapyl alcohols), oligomers, and polymers. Whereas plant peroxidases have been shown to catalyze oxidative coupling of monolignols, the oxidation activity of well-studied plant peroxidases, such as horseradish peroxidase C (HRP-C) and AtPrx53, are quite low for sinapyl alcohol. This characteristic difference has led to controversy regarding the oxidation mechanism of sinapyl alcohol and lignin oligomers and polymers by plant peroxidases. The present study explored the oxidation activities of three plant peroxidases, AtPrx2, AtPrx25, and AtPrx71, which have been already shown to be involved in lignification in the Arabidopsis stem. Recombinant proteins of these peroxidases (rAtPrxs) were produced in Escherichia coli as inclusion bodies and successfully refolded to yield their active forms. rAtPrx2, rAtPrx25, and rAtPrx71 were found to oxidize two syringyl compounds (2,6-dimethoxyphenol and syringaldazine), which were employed here as model monolignol compounds, with higher specific activities than HRP-C and rAtPrx53. Interestingly, rAtPrx2 and rAtPrx71 oxidized syringyl compounds more efficiently than guaiacol. Moreover, assays with ferrocytochrome c as a substrate showed that AtPrx2, AtPrx25, and AtPrx71 possessed the ability to oxidize large molecules. This characteristic may originate in a protein radical. These results suggest that the plant peroxidases responsible for lignin polymerization are able to directly oxidize all lignin precursors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / enzymology*
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / isolation & purification
  • Biocatalysis
  • Catalytic Domain
  • Cytochromes c / chemistry
  • Guaiacol / chemistry
  • Hydrazones / chemistry
  • Lignin / biosynthesis*
  • Models, Molecular
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Peroxidases / chemistry*
  • Peroxidases / isolation & purification
  • Plant Stems / enzymology*
  • Protein Refolding
  • Pyrogallol / analogs & derivatives
  • Pyrogallol / chemistry

Substances

  • Arabidopsis Proteins
  • Hydrazones
  • Pyrogallol
  • syringaldazine
  • pyrogallol 1,3-dimethyl ether
  • Guaiacol
  • Lignin
  • Cytochromes c
  • Peroxidases
  • Prx2 protein, Arabidopsis
  • Prx25 protein, Arabidopsis
  • Prx71 protein, Arabidopsis

Grant support

This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI (B) Grant Number 23380102 (Y.T.) and JSPS KAKENHI Young Scientists (B) Grant Number 25850123 (J.S.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.