A Novel NAD+-dependent Aldehyde Dehydrogenase Encoded by the puuC Gene of Klebsiella pneumoniae DSM 2026 that Utilizes 3-Hydroxypropionaldehyde as a Substrate

3-Hydroxypropionic acid (3-HP), a versatile and valuable platform chemical, has diverse industrial applications; but its biological production from glycerol is often limited by the capability of the enzyme aldehyde dehydrogenase (ALDH) to convert an intermediary compound, 3-hydroxypropionaldehyde (3-HPA), to 3-HP. In this study, we report a new ALDH, PuuC, from Klebsiella pneumoniae DSM 2026, that efficiently converts 3-HPA to 3-HP. The identified gene puuC was cloned, expressed in Escherichia coli, purified, and characterized for its properties. The recombinant enzyme with a molecular weight of 53.8 kDa exhibited broad substrate specificity for various aliphatic aldehydes, especially C-2-C-5 aldehydes. NAD(+) was the preferred coenzyme for the oxidation of most aliphatic and aromatic aldehydes tested. The optimum pH and temperature for PuuC activity were pH 8.0 and 45 degrees C. The K-m values for 3-HPA and NAD(+) were 0.48 and 0.09 mM, respectively. The activity of PuuC was enhanced in the presence of reducing agents such as 2-mercaptoethanol or dithiothreitol, while several metal ions, particularly Hg2+, Ag+, and Cu2+ inhibited its activity. The predicted structure of PuuC indicated the presence of K191 and E194 in close proximity to the glycine motif, suggesting that PuuC belongs to class 2 ALDHs. (C) KSBB