Saturation-mutagenesis in two positions distant from active site of a Klebsiella pneumoniae glycerol dehydratase identifies some highly active mutants

Synthesis of 1,3-propanediol (1,3-PD) from glycerol through the biotransformation process requires two steps, catalyzed by glycerol dehydratase (GDHt) and 1,3-PD oxidoreductase. GDHt is the rate-limiting enzyme in this process. All recombinant microorganisms for production of 1,3-PD so far utilized the natural genes that may not have been optimized. Two positions, which are 19.3 Å and 29.6 Å away from the active site in GDHt from Klebsiella pneumoniae, were subjected to saturation-mutagenesis and 38 mutants were characterized. The catalytic activity of a mutant in β-subunit (β-Q42F, 29.6 Å from the active site) was 8.3-fold higher than the wild type, and the enzyme efficiency of other two mutants β-Q42L and β-Q42S for substrate glycerol was 336-fold and 80-fold higher than that for 1,2-propanediol. This investigation supplied further evidence that distant mutations could be a good source of diversity and therefore, made a contribution to the toolbox of industrial enzyme improvement.