Cloning and functional expression of glucose dehydrogenase complex of Burkholderia cepacia in Escherichia coli

The thermostable glucose dehydrogenase (GDH) from Burkholderia cepacia sp. SM4 is composed of a catalytic subunit (α), an electron transfer subunit (β), and a small γ subunit of unknown function. We cloned a 1428-nucleotide gene encoding the β subunit located immediately downstream of the α subunit. This completes the isolation of the genes encoding the three components of the GDH complex, which are clustered very close together with the same transcription polarity in the order γαβ. The deduced β subunit amino acid sequence contains three typical heme-binding motifs and was 44–49% identical to the cytochrome c subunits of other FAD-dependent dehydrogenase complexes. The GDHγαβ complex of B. cepacia was successfully expressed in a fully active form in Escherichia coli by co-expression with cytochrome c maturation genes. Recombinant expression of the GDH complex was also found to restore glucose-dependent respiration in a GDH mutant of E. coli.