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Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases.

ABSTRACT: Tyrosinases and catechol oxidases belong to the polyphenol oxidase (PPO) enzyme family, which is mainly responsible for the browning of fruits. Three cDNAs encoding PPO pro-enzymes have been cloned from leaves of Malus domestica (apple, MdPPO). The three pro-enzymes MdPPO1-3 were heterologously expressed in E. coli yielding substantial amounts of protein and have been characterized with regard to their optimum of activity resulting from SDS, acidic and proteolytic activation. Significant differences were found in the kinetic characterization of MdPPO1-3 when applying different mono- and diphenolic substrates. All three enzymes have been classified as tyrosinases, where MdPPO1 exhibits the highest activity with tyramine (kcat?=?9.5?s-1) while MdPPO2 and MdPPO3 are also clearly active on this monophenolic substrate (kcat?=?0.92?s-1 and kcat?=?1.0?s-1, respectively). Based on the activity, sequence data and homology modelling it is proposed that the monophenolase and diphenolase activity of PPOs can be manipulated by the appropriate combination of two amino acids, which are located within the active site cleft and were therefore named "activity controllers".

SUBMITTER: Kampatsikas I

PROVIDER: S-EPMC5562730 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases.

Kampatsikas Ioannis I Bijelic Aleksandar A Pretzler Matthias M Rompel Annette A

Scientific reports 20170818 1

Tyrosinases and catechol oxidases belong to the polyphenol oxidase (PPO) enzyme family, which is mainly responsible for the browning of fruits. Three cDNAs encoding PPO pro-enzymes have been cloned from leaves of Malus domestica (apple, MdPPO). The three pro-enzymes MdPPO1-3 were heterologously expressed in E. coli yielding substantial amounts of protein and have been characterized with regard to their optimum of activity resulting from SDS, acidic and proteolytic activation. Significant differe ...[more]

PMID: 28821733

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Project description:Polyphenol oxidases (PPOs) catalyze the oxidation of phenolics to quinones, the secondary reactions of which lead to oxidative browning and postharvest losses of many fruits and vegetables. PPOs are ubiquitous in angiosperms, are inducible by both biotic and abiotic stresses, and have been implicated in several physiological processes including plant defense against pathogens and insects, the Mehler reaction, photoreduction of molecular oxygen by PSI, regulation of plastidic oxygen levels, aurone biosynthesis and the phenylpropanoid pathway. Here we review experiments in which the roles of PPO in disease and insect resistance as well as in the Mehler reaction were investigated using transgenic tomato (Lycopersicon esculentum) plants with modified PPO expression levels (suppressed PPO and overexpressing PPO). These transgenic plants showed normal growth, development and reproduction under laboratory, growth chamber and greenhouse conditions. Antisense PPO expression dramatically increased susceptibility while PPO overexpression increased resistance of tomato plants to Pseudomonas syringae. Similarly, PPO-overexpressing transgenic plants showed an increase in resistance to various insects, including common cutworm (Spodoptera litura (F.)), cotton bollworm (Helicoverpa armigera (Hübner)) and beet army worm (Spodoptera exigua (Hübner)), whereas larvae feeding on plants with suppressed PPO activity had higher larval growth rates and consumed more foliage. Similar increases in weight gain, foliage consumption, and survival were also observed with Colorado potato beetles (Leptinotarsa decemlineata (Say)) feeding on antisense PPO transgenic tomatoes. The putative defensive mechanisms conferred by PPO and its interaction with other defense proteins are discussed. In addition, transgenic plants with suppressed PPO exhibited more favorable water relations and decreased photoinhibition compared to nontransformed controls and transgenic plants overexpressing PPO, suggesting that PPO may have a role in the development of plant water stress and potential for photoinhibition and photooxidative damage that may be unrelated to any effects on the Mehler reaction. These results substantiate the defensive role of PPO and suggest that manipulation of PPO activity in specific tissues has the potential to provide broad-spectrum resistance simultaneously to both disease and insect pests, however, effects of PPO on postharvest quality as well as water stress physiology should also be considered. In addition to the functional analysis of tomato PPO, the application of antisense/sense technology to decipher the functions of PPO in other plant species as well as for commercial uses are discussed.

Project description:γδ T cells are lymphocytes that function in both innate and adaptive immune responses, and our laboratory has previously reported that both bovine and human γδ T cells are primed for secondary responses by tannin components of the unripe apple peel (APP). In this report we began to investigate the mechanism by which priming occurs. We performed a microarray analysis on sorted bovine γδ T cells treated with APP and observed significant increases in transcripts encoding select inflammatory cytokines, such as GM-CSF, IL-8, and IL-17, but not markers of TCR stimulation such as IFNγ. When injected into the gut of mice, APP induced a robust influx of neutrophils into both the blood and peritoneum as measured by FACS. Importantly, both GM-CSF and IL-8 proteins were detected in these animals. Further studies were performed using the human γδ T cell-line MOLT-14, as large numbers of cells were required for subsequent experiments. Using these cells we found that both the GM-CSF and IL-8 mRNAs were significantly upregulated and stabilized in cells treated with APP. Finally, we show that the ERK1/2 MAPK pathway was activated in APP-treated MOLT-14 cells, and that this pathway plays a role in the mRNA stabilization we observed. Together, our data describe a unique inflammatory response in bovine, murine, and human γδ T cells in response to APP, and suggest that mRNA stability mechanisms could account for the priming phenotype we previously observed.APP has a distinctive gamma delta T cells specific priming activity. Keywords: comparison of 2 treatment types, tannin, gamma delta T cells To begin to understand the effects of APP in innate immunity, we investigated the global gene expression profiles of stimulated bovine gamma delta T cells. Peripheral blood from 2 neonatal bovine calves was collected. gamma delta T cells were sorted to >97% purity using a FACS Vantage. Cells were placed in culture and stimulated with either an aqueous extract of APP (42.2ug/ml) or PBS for 4 hours after which RNA was extracted and processed for microarray analysis following standard protocols from Affymetrix.

Dataset Information

Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases.

Publications

Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases.

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