Characterization of two forms of cationic peroxidase from cultured peanut cells

Removal of the N-linked glycan structure from the peanut peroxidase prxPNC2: influence on protein stability and activity

Lines of transgenic tobacco have been generated that are transformed with either the wild-type peanut peroxidase prxPNC2 cDNA, driven by the CaMV35S promoter (designated 35S::prxPNC2-WT) or a mutated PNC2 cDNA in which the asparagine residue (Asn189) associated with the point of glycan attachment (Asn189) has been replaced with alanine (designated 35S::prxPNC2-M). PCR, using genomic DNA as template, has confirmed the integration of the 35S::prxPNC2-WT and 35S:prxPNC2-M constructs into the tobacco genome, and western analysis using anti-PNC2 antibodies has revealed that the prxPNC2-WT protein product (PNC2-WT) accumulates with a molecular mass of 34,670 Da, while the prxPNC2-M protein product (PNC2-M) accumulates with a molecular mass of 32,600 Da. Activity assays have shown that both PNC2-WT and PNC2-M proteins accumulate preferentially in the ionically-bound cell wall fraction, with a significantly higher relative accumulation of the PNC2-WT isoenzyme in the ionically-bound fraction when compared with the PNC2-M isoform. Kinetic analysis of the partially purified PNC2-WT isozyme revealed an affinity constant (apparent Km) of 11.2 mM for the reductor substrate guaiacol and 1.29 mM for H2O2, while values of 11.9 mM and 1.12 mM were determined for the PNC2-M isozyme. A higher Arrenhius activation energy (Ea) was determined for the PNC2-M isozyme (22.9 kJ mol(-1)), when compared with the PNC2-WT isozyme (17.6 kJ mol(-1)), and enzyme assays have determined that the absence of the glycan influences the thermostability of the PNC2-M isozyme. These results are discussed with respect to the proposed roles of N-linked glycans attached to plant peroxidases.

Investigation of cationic peanut peroxidase glycans by electrospray ionization mass spectrometry

Cationic peanut peroxidase (CP) was isolated from peanut (Arachis hypogaea) cell suspension culture medium. CP is a glycoprotein with three N-linked glycan sites at Asn60, Asn144, and Asn185. ESI-MS of the intact purified protein reveals the microheterogeneity of the glycans. Tryptic digestion of CP gave a near complete sequence coverage by ESI-MS. The glycopeptides from the tryptic digestion were separated by RP HPLC identified by ESI-MS and the structure of the glycan chains determined by ESI-MS/MS. The glycans are large structures of up to 16 sugars, but most of their non-reducing ends have been modified giving a mixture of shorter chains at each site. Good agreement was found with the one glycan previously analyzed by (1)H NMR. This work is the basis for the future studies on the role of the glycans on stability and folding of CP and is another example of a detailed structural characterization of complex glycoproteins by mass spectrometry.

A retrospective look at the cationic peanut peroxidase structure

The cationic peanut peroxidase has been studied in detail, not only with regard to its peptide structure, but also to the sites and role of the three moieties linked to it. Peanut peroxidase lends itself well to a close examination as a potential example for other plant peroxidase studies. It was the first plant peroxidase for which a 3-D structure was derived from crystals, with the glycans intact. Subsequent analysis of peroxidases structures from other plants have not shown great differences to that of the peanut peroxidase. As the period of proteomics follows on the era of genomics, the study of glycans has been brought back into focus. With the potential use of peroxidase as a polymerization agent for industry, there are some aspects of the overall structure that should be kept in mind for successful use of this enzyme. A variety of techniques are now available to assay for these structures/moieties and their roles. Peanut peroxidase data are reviewed in that light, as well as defining some true terms for isozymes. Because a high return of the enzyme in a pure form has been obtained from cultured cells in suspension culture, a brief review of this is also offered.

Scots pine expresses short-root-specific peroxidases during development

Nine short-root-specific proteins from Scots pine (Pinus sylvestris L.) detected and isolated as individual spots by 2D-PAGE were identified. The similar peptide mass maps obtained for all nine polypeptide spots together with lectin-blotting results suggest that they represent forms of the same modified protein. N-Terminal sequence analysis of two of the peptides showed high similarity to peroxidases. RT-PCR with oligonucleotide primers corresponding to determined peptide sequences and conserved regions in plant peroxidases led to isolation of Psyp1 cDNA which is most abundantly expressed in short roots. Psyp1 is the first peroxidase cDNA to be isolated from the genus Pinus. It encodes a 363-amino-acid class-III peroxidase with a calculated molecular mass of 35.7 kDa and theoretical pI of 4.74. The predicted PSYP1 amino-acid sequence is grouped with other class-III peroxidases in phylogenetic analyses, but it has a unique amino-acid sequence which may be associated with its function in short roots or with its phylogenetic group. The presence of a signal sequence for extracellular transport indicates that PSYP1 belongs to the group of secreted class-III peroxidases. The presence of 10 tyrosine residues and putative auxin-binding regions in PSYP1 suggests that the function of the enzyme is associated with cell-wall formation in short roots. The downregulation of Psyp1 expression in symbiotic short roots hosting the ectomycorrhizal fungus Suillus bovinus is perhaps related to the change in cell-wall structure necessary for ectomycorrhizal development.

A 37-kDa peroxidase secreted from liverworts in response to chemical stress

A peroxidase was purified from the culture medium of a suspension culture of Marchantia polymorpha (liverwort) after treatment with bornyl acetate, which acts as a chemical stress agent to the cells. The peroxidase was characterised as a glycoprotein of molecular mass 37-kDa having a pl of about 10 and an optimal pH of 6.5. The peroxidase was thermally stable at 50 degrees C for up to 60 min. The partial amino acid sequence of the peroxidase was determined and found to be dissimilar to the amino acid sequences of other higher plant peroxidases. The oxidative polymerization of lunularin by this peroxidase was examined and the formation of a dimer, a trimer and a tetramer was demonstrated by negative ion Fast Atom Bombardment (FAB)-mass spectroscopy of the reaction products.

Sequence specific analysis of the heterogeneous glycan chain from peanut peroxidase by 1H-NMR spectroscopy

The cationic peanut peroxidase is a complex enzyme consisting of a heme group, two calcium ions and three complex carbohydrate chains at positions Asn60, 144 and 185. Details of the heme and calcium ligation, necessary for oxidation, have recently been revealed from the three-dimensional structure of the peroxidase. However, the three glycans that may be important for the stability of the enzyme as well as its activity were not resolved. In order to determine the configuration of one of these glycans, PNGase A was used to cleave the glycan from the enzyme at Asn-144. This glycan was studied by two dimensional 1H-NMR spectroscopy to identify the sugar linkages. The results indicated a glycan structure comprising a Man alpha1-6(Xyl beta1-2)Man beta1-4GlcNAc beta1-4(Fuc alpha1-3)GlcNAc beta core but with an additional Man alpha1-3 appendage linked to Man3. The glycan also appeared to be heterogeneous as was noted from a single terminating galactose being linked to approximately 20-25% glycan.

Biochemical characterization of the suberization-associated anionic peroxidase of potato

The anionic peroxidase associated with the suberization response in potato (Solanum tuberosum L.) tubers during wound healing has been purified and partially characterized at the biochemical level. It is a 45-kD, class III (plant secretory) peroxidase that is localized to suberizing tissues and shows a preference for feruloyl (o-methoxyphenol)-substituted substrates (order of substrate preference: feruloyl > caffeoyl > p-coumaryl approximately syringyl) such as those that accumulate in tubers during wound healing. There was little influence on oxidation by side chain derivatization, although hydroxycinnamates were preferred over the corresponding hydroxycinnamyl alcohols. The substrate specificity pattern is consistent with the natural substrate incorporation into potato wound suberin. In contrast, the cationic peroxidase(s) induced in response to wound healing in potato tubers is present in both suberizing and nonsuberizing tissues and does not discriminate between hydroxycinnamates and hydroxycinnamyl alcohols. A synthetic polymer prepared using E-[8-(13)C]ferulic acid, H(2)O(2), and the purified anionic enzyme contained a significant amount of cross-linking through C-8, albeit with retention of unsaturation.

Glycans of higher plant peroxidases: recent observations and future speculations

Plant peroxidases are composed of a peptide and associated heme, calcium and glycans. The 3D structure of the major cationic peanut peroxidase has revealed the sites of the heme and calcium. But the diffraction of the glycans was not sufficient to show their structure. This review presents research that has been executed to obtain putative glycans and their binding sites, and to gain an indirect insight into these glycans. It also offers approaches that will be used to determine the function of the glycans on the peanut peroxidase. Some comparisons are made with other plant glycoproteins including peroxidases from plants other than peanut.

Characterization of anionic soybean (Glycine max) seed coat peroxidase

Soybean (Glycine max) seed coats may contain large amounts of peroxidase enzyme. The release of peroxidase from whole seeds upon imbibition and the catalytic and antigenic properties of this enzyme were studied. Comparisons between high (Ep) and low (epep) peroxidase activity seeds demonstrated a lengthy (336 h) release of anionic peroxidase by Ep (Harovinton) cultivars following incubation in an aqueous environment. In its purified state, soybean seed coat peroxidase exhibited good catalytic activity towards phenolic substrates including eugenol, caffeic acid, and ferulic acid. Both leaf and stem cationic peroxidases behaved similarly to seed coat peroxidase in their substrate specificity. Furthermore, using guaiacol as a substrate at various pH levels and temperatures, soybean seed coat peroxidase had a greater enzyme stability and a wider range of action than other peroxidase enzymes. Polyclonal antibodies raised against cationic peanut peroxidase cross-reacted with soybean peroxidase in the presence and the absence of its glycosidic chains. This suggests homology in epitopes between the soybean and peanut polypeptide and (or) glycan chains. Key words: cross-reactivity, enzyme activity, peroxidase, polymerization, substrate.

Immunogenicity of the N-glycans of peanut peroxidase

The three tryptic glycopeptides of cationic peanut peroxidase (C. PRX) and the sole one of anionic peanut peroxidase (A. PRX) were individually coupled to bovine serum albumin to raise antisera. The three categories of antibodies directed towards three N-glycans of C. PRX (anti-GLa, anti-GLb and anti-GLc) were isolated from antisera with glycan-conjugated ECH Sepharose 4B affinity columns and the distribution of epitopes on the N-glycans was investigated. The reactivity of anti-GLa, anti-GLb and anti-GLc is inhibited 25-40% by 1 M fucose, compared with a slight inhibition by N-acetylglycosamine and xylose. Mannose and galactose showed no inhibition to anti-GLa and only a slight inhibition to anti-GLb and anti-GLc. All of anti-GLa, anti-GLb and anti-GLc recognize A. PRX and horseradish peroxidase but do not recognize fetuin. Also, their reactivity is inhibited by bromelain by more than 70%. The three categories of antibodies present high homogeneity and appear to be directed mainly towards the core structure [Xyl] (Man)3 [Fuc] (GlcNAc)2. An effective and simple method to screen antibodies with carbohydrate specificities is described herein.