Quinoprotein ethanol dehydrogenase of Pseudomonas aeruginosa is a homodimer -: Sequence of the gene and deduced structural properties of the enzyme

The gene coding for the periplasmic quinoprotein ethanol dehydrogenase of Pseudomonas aeruginosa ATCC 17933 was cloned and sequenced. The deduced amino acid sequence contained a signal peptide of 34 residues and the major protein of 589 amino acids showed high similarities to pyrroloquinoline-quinone-dependent periplasmic and membrane-bound dehydrogenases acting on alcohols, glucose and quinate or shikimate. It was demonstrated by alignment with the amino acid sequence of the large subunit of the quinoprotein methanol dehydrogenase from Methylobacterium extorquens, whose X-ray structure is known, that the amino acid residues involved in the binding of pyrroloquinoline quinone and Ca2+ at the active site are conserved in the quinoprotein ethanol dehydrogenase of P. aeruginosa. Also, the glycine/tryptophan docking motifs involved in stabilizing the superbarrel structure of the quinoprotein methanol dehydrogenase of M. extorquens were conserved. The known sequences of pyrroloquinoline-quinone-dependent dehydrogenases were used to derive new, more specific sequence motifs for detecting members of this family of enzymes. Despite the sequence similarity between the large cc subunit of quinoprotein methanol dehydrogenase from M. extorquens and the quinoprotein ethanol dehydrogenase from P. aeruginosa, the two enzyme systems were quite different. In the presence of the prosthetic group, pyrroloquinoline quinone expression of the Pseudomonas gene encoding the 60-kDa subunit of quinoprotein ethanol dehydrogenase in Escherichia coli resulted in formation of active enzyme. The formation of active quinoprotein methanol dehydrogenase, however, is known to require, in addition to the large cc subunit, the expression of a small beta subunit, and helper proteins [Lidstrom, M. E. (1995) Genetics of bacterial quinoproteins, Methods Enzymol. 258, 217-227].