Discovery and investigation of a new, second triose phosphate isomerase in Klebsiella pneumoniae

In this study, a tpi1 gene encoding for the enzyme triose phosphate isomerase in Klebsiella pneumoniae DSM2026 was knocked out in an effort to metabolically engineer this strain as a model system for the production of 1,3-propanediol. Investigations of the tpi1 knockout mutant led to the discovery of a second tpi gene (tpi2) in this organism. The new tpi2 gene was cloned and sequenced. The coding region of the tpi2 gene contains 795bp (base pairs) and the deduced protein consists of 265 amino acids. Sequence comparison of TPI2 proteins in different organisms revealed the presence of a highly conserved signature A-Y-E-P-V-W-A-I-G-[EDVS]-[GKNASH], which is nearly the same as the reported TPI consensus signature. The tpi1 gene of K. pneumoniae DSM2026 shows a high sequence similarity to that of E. coli, whereas, the tpi2 gene resembles more its relatives in the alpha-proteobacteria, suggesting that they evolve from different ancestors. The overexpression of the tpi2 gene restores the growth deficiency of tpi1 knockout mutant on the minimal medium containing glucose or glycerol. Furthermore, the catalytic activity of this new triose phosphate isomerase was confirmed in both tpi1 knockout mutant and tpi2 over-expressing strain by enzyme assays. For the first time, the co-existence of two tpi genes in an enteric bacterium is experimentally confirmed.