Abstract
Diverse ascomycete fungi oxidize manganese(II) [Mn(II)] and produce Mn(III, IV) oxides in terrestrial and freshwater environments. Although multicopper oxidase (MCO) is considered to be a key catalyst in mediating Mn(II) oxidation in ascomycetes, the responsible gene and its product have not been identified. In this study, a gene, named mco1, encoding Mn(II)-oxidizing MCO from Acremonium strictum strain KR21-2 was cloned and heterologously expressed in the methylotrophic yeast Pichia pastoris. Based on the phylogenetic relationship, similarity of putative copper-binding motifs, and homology modeling, the gene product Mco1 was assigned to a bilirubin oxidase. Mature Mco1 was predicted to be composed of 565 amino acids with a molecular mass of 64.0 kDa. The recombinant enzyme oxidized Mn(II) to yield spherical Mn oxides, several micrometers in diameter. Zinc(II) ions added to the reaction mixture were incorporated by the Mn oxides at a Zn/Mn molar ratio of 0.36. The results suggested that Mco1 facilitates the growth of the micrometer-sized Mn oxides and affects metal sequestration through Mn(II) oxidation. This is the first report on heterologous expression and identification of the Mn(II) oxidase enzyme in Mn(II)-oxidizing ascomycetes. The cell-free, homogenous catalytic system with recombinant Mco1 could be useful for understanding Mn biomineralization by ascomycetes and the sequestration of metal ions in the environment
Highlights
Several microorganisms can convert manganese(II) [Mn(II)] to insoluble Mn(III, IV) oxides and are responsible for Mn deposition in natural environments [1]
multicopper oxidase (MCO) are considered to be Mn oxidases in ascomycetes, the present study indicated that the enzyme from strain KR21-2 belonged to a different class of MCOs
The genome of A.Gene strictum strain KR21-2 was analyzed by whole-genome shotgun sequencing
Summary
Several microorganisms can convert manganese(II) [Mn(II)] to insoluble Mn(III, IV) oxides and are responsible for Mn deposition in natural environments [1]. Biogenic Mn oxides serve as fine adsorbents for cationic species and as oxidants for redox-sensitive elements, implying their important role in the geochemical cycles of numerous elements [1,2]. Based on these functions, microbial Mn(II) oxidation has attracted attention. Since Mn oxides serve as an oxidant of organic compounds, recent studies have focused on using biogenic. Studies on catalytic oxidation of Mn(II) by microorganisms are of growing significance, because of such geochemical implications of Mn minerals and due to its biotechnological applicability
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