A Membrane-Bound Gluconate Dehydrogenase from 2-Keto-d-Gluconic Acid Industrial Producing Strain Pseudomonas plecoglossicida JUIM01: Purification, Characterization, and Gene Identification

The membrane-bound gluconate dehydrogenase (mGADH) is a critical enzyme for 2-keto-d-gluconic acid (2KGA) production in Pseudomonas plecoglossicida JUIM01. The purified native flavin adenine dinucleotide-dependent mGADH (FAD-mGADH) was consisted of a gamma subunit, a flavoprotein subunit, and a cytochrome c subunit with molecular mass of similar to 27, 65, and 47kDa, respectively. The specific activity of FAD-mGADH was determined as 90.71U/mg at optimum pH and temperature of 6.0 and 35 degrees C. The K-m and V-max values of calcium d-gluconate were 0.631mM and 0.734mM/min. The metal ions Mg2+ and Mn2+ showed slight positive effects on FAD-mGADH activity. On the other hand, a 3868-bp-length gad gene cluster was amplified and expressed in Escherichia coli BL21(DE3). The recombinant protein showed the same molecular weight and enzyme activity as the native FAD-mGADH, which confirmed it as a FAD-mGADH encoding gene. The flavoprotein subunit and the cytochrome c subunit containing a putative FAD-binding motif and three possible heme-binding motifs concluded from alignment results of mGADHs. This study characterized the native and recombinant FAD-mGADH and would provide the basis for further genetic modification of Pseudomonas plecoglossicida JUIM01 with the intention of 2KGA productivity improvement.