Characterization and heterologous expression of the oxalyl-CoA decarboxylase gene from Bifidobacterium lactis

Oxalyl coenzyme A (CoA) decarboxylase (Oxc) is a key enzyme in the catabolism of the highly toxic
compound oxalate, catalyzing the decarboxylation of oxalyl-CoA to formyl-CoA. The gene encoding a novel
oxalyl-CoA decarboxylase from Bifidobacterium lactis DSM 10140 (oxc) was identified and characterized. This
strain, isolated from yogurt, showed the highest oxalate-degrading activity in a preliminary screening with 12
strains belonging to Bifidobacterium, an anaerobic intestinal bacterial group largely used in probiotic products.
The oxc gene was isolated by probing a B. lactis genomic library with a probe obtained by amplification of the
oxalyl-CoA decarboxylase gene from Oxalobacter formigenes, an anaerobic bacterium of the human intestinal
microflora. The oxc DNA sequence analysis revealed an open reading frame of 1,773 bp encoding a deduced
590-amino-acid protein with a molecular mass of about 63 kDa. Analysis of amino acid sequence showed a
significant homology (47%) with oxalyl-CoA decarboxylase of O. formigenes and a typical thiamine pyrophosphate-
binding site that has been reported for several decarboxylase enzymes. Primer extension experiments
with oxc performed by using RNA isolated from B. lactis identified the transcriptional start site 28 bp upstream
of the ATG start codon, immediately adjacent to a presumed promoter region. The protein overexpressed in
Escherichia coli cross-reacted with an anti-O. formigenes oxalyl-CoA decarboxylase antibody. Enzymatic activity,
when evaluated by capillary electrophoresis analysis, demonstrated that the consumption substrate oxalyl-CoA
was regulated by a product inhibition of the enzyme. These findings suggest a potential role for Bifidobacterium
in the intestinal degradation of oxalate.
Oxalate is ubiquitous in the plant kingdom and is consumed