Oxalate decarboxylase of the white-rot fungus Dichomitus squalens demonstrates a novel enzyme primary structure and non-induced expression on wood and in liquid cultures.
Oxalate decarboxylase (ODC) catalyses the conversion of oxalic acid to formic acid and CO(2) in bacteria and fungi. In wood-decaying fungi the enzyme has been linked to the regulation of intra- and extracellular quantities of oxalic acid, which is one of the key components in biological decomposition of wood. ODC enzymes are biotechnologically interesting for their potential in diagnostics, agriculture and environmental applications, e.g. removal of oxalic acid from industrial wastewaters. We identified a novel ODC in mycelial extracts of two wild-type isolates of Dichomitus squalens, and cloned the corresponding Ds-odc gene. The primary structure of the Ds-ODC protein contains two conserved Mn-binding cupin motifs, but at the N-terminus, a unique, approximately 60 aa alanine-serine-rich region is found. Real-time quantitative RT-PCR analysis confirmed gene expression when the fungus was cultivated on wood and in liquid medium. However, addition of oxalic acid in liquid cultures caused no increase in transcript amounts, thereby indicating a constitutive rather than inducible expression of Ds-odc. The detected stimulation of ODC activity by oxalic acid is more likely due to enzyme activation than to transcriptional upregulation of the Ds-odc gene. Our results support involvement of ODC in primary rather than secondary metabolism in fungi.
Mäkelä
Miia R
MR
Department of Applied Chemistry and Microbiology, Division of Microbiology, Viikki Biocenter, PO Box 56, FIN-00014 University of Helsinki, Finland.
Hildén
Kristiina
K
Department of Applied Chemistry and Microbiology, Division of Microbiology, Viikki Biocenter, PO Box 56, FIN-00014 University of Helsinki, Finland.
Hatakka
Annele
A
Department of Applied Chemistry and Microbiology, Division of Microbiology, Viikki Biocenter, PO Box 56, FIN-00014 University of Helsinki, Finland.
Lundell
Taina K
TK
Department of Applied Chemistry and Microbiology, Division of Microbiology, Viikki Biocenter, PO Box 56, FIN-00014 University of Helsinki, Finland.
D000595:Amino Acid Sequence; D001483:Base Sequence; D002262:Carboxy-Lyases / Q000096:biosynthesis* / Q000235:genetics* / Q000302:isolation & purification; D003470:Culture Media / Q000378:metabolism; D004271:DNA, Fungal / Q000096:biosynthesis / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D019815:Oxalic Acid / Q000378:metabolism; D011124:Polyporaceae / Q000201:enzymology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation; D014934:Wood / Q000378:metabolism
D003470:Culture Media; D004271:DNA, Fungal; D019815:Oxalic Acid; D002262:Carboxy-Lyases; C021915:oxalate decarboxylase