serovar Typhimurium has three transketolase enzymes contributing to the pentose phosphate pathway.

The genus is responsible for many illnesses in humans and other vertebrate animals. We report here that serovar Typhimurium harbors three transketolases that support the non-oxidative branch of the pentose phosphate pathway. BLAST analysis identified two genes, _ and _, that together encode a putative transketolase (TktC) with 46-47% similarity to the known TktA and TktB isoforms. Assessing the mRNA and protein expression for each of the three transketolases, we determined that all are expressed in WT cells and regulated to varying extents by the alternative sigma factor RpoS. Enzyme assays with lysates from WT and transketolase-knockout strains established that TktA is responsible for >88% of the transketolase activity in WT cells. We purified recombinant forms of each isoenzyme to assess the kinetics for canonical transketolase reactions. TktA and TktB had comparable values for (539-1362 μm NADH consumed/s), (80-739 μm), and catalytic efficiency (1.02 × 10-1.06 × 10 m/s) for each substrate tested. The recombinant form of TktC had lower values (23-120 μm), whereas the (7.8-16 μm NADH consumed/s) and catalytic efficiency (5.58 × 10 to 6.07 × 10 m/s) were 10-100-fold lower. Using a murine model of infection, we showed that a strain lacking all three transketolases is avirulent in C57BL/6 mice. These data provide evidence that Typhimurium possesses three transketolases that contribute to pathogenesis.