Purification, characterization and gene identification of a membrane-bound glucose dehydrogenase from 2-keto-d-gluconic acid industrial producing strain Pseudomonas plecoglossicida JUIM01.

The membrane-bound glucose dehydrogenase (mGDH) is a rate-limiting enzyme for the industrial production of 2-keto-d-gluconic acid (2KGA) from glucose. In this study, mGDH was firstly purified from a 2KGA industrial producing strain Pseudomonas plecoglossicida JUIM01. The purified mGDH exhibited a specific activity of 16.85 U/mg and was identified as monomeric membrane-bound PQQ-dependent dehydrogenase with a molecular mass of ~87 kDa. The K and V value of d-glucose were 0.042 mM and 14.620 μM/min, and the optimal pH and temperature were of 6.0 and 35 °C with favorable acid resistance and poor heat tolerance. Ca/Mg showed a significantly positive effect on mGDH activity with 20% increase, whereas EDTA/EGTA had a negative influence, and Ca was essential for enzyme activity. Furthermore, a 2412 bp-length gcd was amplified by genome walking technique and heterologously expressed in Escherichia coli. Bioinformatics analysis and heterologous expression further confirmed it as a mGDH encoding gene. mGDH contained binding sites of Ca, cofactor PQQ and polypeptide binding sites concluded from alignment results of mGDHs from different genera. This study would lay the foundation for improving 2KGA productivity through further strain modification.