A Fungal Ascorbate Oxidase with Unexpected Laccase Activity.
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ABSTRACT:
SUBMITTER: Braunschmid V
PROVIDER: S-EPMC7460845 | biostudies-literature | 2020 Aug
REPOSITORIES: biostudies-literature
Publications
A Fungal Ascorbate Oxidase with Unexpected Laccase Activity.
Braunschmid Verena V Fuerst Sarah S Perz Veronika V Zitzenbacher Sabine S Hoyo Javier J Fernandez-Sanchez Cesar C Tzanov Tzanko T Steinkellner Georg G Gruber Karl K Nyanhongo Gibson S GS Ribitsch Doris D Guebitz Georg M GM
International journal of molecular sciences 20200811 16
Ascorbate oxidases are an enzyme group that has not been explored to a large extent. So far, mainly ascorbate oxidases from plants and only a few from fungi have been described. Although ascorbate oxidases belong to the well-studied enzyme family of multi-copper oxidases, their function is still unclear. In this study, <i>Af</i>_AO1, an enzyme from the fungus <i>Aspergillus flavus</i>, was characterized. Sequence analyses and copper content determination demonstrated <i>Af</i>_AO1 to belong to t ...[more]
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Project description:Members of the multicopper oxidase (MCO) family of enzymes can be classified by their substrate specificity; for example, ferroxidases oxidize ferrous iron, ascorbate oxidases oxidize ascorbate, and laccases oxidize aromatic substrates such as diphenols. Our previous work on an insect multicopper oxidase, MCO1, suggested that it may function as a ferroxidase. This hypothesis was based on three lines of evidence: RNAi-mediated knock down of Drosophila melanogaster MCO1 (DmMCO1) affects iron homeostasis, DmMCO1 has ferroxidase activity, and DmMCO1 has predicted iron binding residues. In our current study, we expanded our focus to include MCO1 from Anopheles gambiae, Tribolium castaneum, and Manduca sexta. We verified that MCO1 orthologs have similar expression profiles, and that the MCO1 protein is located on the basal surface of cells where it is positioned to oxidize substrates in the hemolymph. In addition, we determined that RNAi-mediated knock down of MCO1 in A. gambiae affects iron homeostasis. To further characterize the enzymatic activity of MCO1 orthologs, we purified recombinant MCO1 from all four insect species and performed kinetic analyses using ferrous iron, ascorbate and two diphenols as substrates. We found that all of the MCO1 orthologs are much better at oxidizing ascorbate than they are at oxidizing ferrous iron or diphenols. This result is surprising because ascorbate oxidases are thought to be specific to plants and fungi. An analysis of three predicted iron binding residues in DmMCO1 revealed that they are not required for ferroxidase or laccase activity, but two of the residues (His374 and Asp380) influence oxidation of ascorbate. These two residues are conserved in MCO1 orthologs from insects and crustaceans; therefore, they are likely to be important for MCO1 function. The results of this study suggest that MCO1 orthologs function as ascorbate oxidases and influence iron homeostasis through an unknown mechanism.
| S-EPMC4387078 | biostudies-literature
Project description:Fungal laccases (EC 1.10.3.2) are multi-copper oxidases that oxidize a wide variety of substrates. Despite extensive studies, the molecular basis for their diverse activity is unclear. Notably, there is no current way to rationally predict the activity of a laccase toward a given substrate. Such knowledge would greatly facilitate the rational design of new laccases for technological purposes. We report a study of three datasets of experimental Km values and activities for Trametes versicolor and Cerrena unicolor laccase, using a range of protein modeling techniques. We identify diverse binding modes of the various substrates and confirm an important role of Asp-206 and His-458 (T. versicolor laccase numbering) in guiding substrate recognition. Importantly, we demonstrate that experimental Km values correlate with binding affinities computed by MMGBSA. This confirms the common assumption that the protein-substrate affinity is a major contributor to observed Km. From quantitative structure-activity relations (QSAR) we identify physicochemical properties that correlate with observed Km and activities. In particular, the ionization potential, shape, and binding affinity of the substrate largely determine the enzyme's Km for the particular substrate. Our results suggest that Km is not just a binding constant but also contains features of the enzymatic activity. In addition, we identify QSAR models with only a few descriptors showing that phenolic substrates employ optimal hydrophobic packing to reach the T1 site, but then require additional electronic properties to engage in the subsequent electron transfer. Our results advance our ability to model laccase activity and lend promise to future rational optimization of laccases toward phenolic substrates.
| S-EPMC6251875 | biostudies-literature
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| S-EPMC1219519 | biostudies-other
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2017-03-01 | E-MTAB-4816 | biostudies-arrayexpress
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Project description:Alcohol oxidases are ecologically important enzymes which facilitate a number of plant-fungal interactions. Within Ascomycota they are primarily associated with methylotrophy, as a peroxisomal alcohol oxidase (AOX) catalyzing the conversion of methanol to formaldehyde in methylotrophic yeast. In this study we demonstrate that AOX orthologs are phylogenetically conserved proteins which are common in the genomes of non-methylotrophic, plant-associating fungi. Additionally, AOX orthologs are highly expressed during infection in a range of diverse pathosystems. To study the role of AOX in plant colonization, AOX knockout mutants were generated in the broad host range pathogen Sclerotinia sclerotiorum. Disease assays in soybean showed that these mutants had a significant virulence defect as evidenced by markedly reduced stem lesions and mortality rates. Chemical genomics suggest that SsAOX may function as an aromatic alcohol oxidase, and growth assays demonstrate that ΔSsAOX is incapable of properly utilizing plant extract as a nutrient source. Profiling of known aromatic alcohols point towards the monolignol coniferyl alcohol (CoA) as a possible substrate for SsAOX. As CoA and other monolignols are ubiquitous among land plants, the presence of highly conserved AOX orthologs throughout Ascomycota imply that this is a broadly conserved protein used by ascomycete fungi during plant colonization.
2022-12-02 | GSE212269 | GEO