High-resolution structures ofLactobacillus salivariustransketolase in the presence and absence of thiamine pyrophosphate

<jats:p>Probiotic bacterial strains have been shown to enhance the health of the host through a range of mechanisms including colonization, resistance against pathogens, secretion of antimicrobial compounds and modulation of the activity of the innate immune system.<jats:italic>Lactobacillus salivarius</jats:italic>UCC118 is a well characterized probiotic strain which survives intestinal transit and has many desirable host-interaction properties. Probiotic bacteria display a wide range of catabolic activities, which determine their competitiveness<jats:italic>in vivo</jats:italic>. Some lactobacilli are heterofermentative and can metabolize pentoses, using a pathway in which transketolase and transaldolase are key enzymes.<jats:italic>L. salivarius</jats:italic>UCC118 is capable of pentose utilization because it encodes the key enzymes on a megaplasmid. The crystal structures of the megaplasmid-encoded transketolase with and without the enzyme cofactor thiamine pyrophosphate have been determined. Comparisons with other known transketolase structures reveal a high degree of structural conservation in both the catalytic site and the overall conformation. This work extends structural knowledge of the transketolases to the industrially and commercially important<jats:italic>Lactobacillus</jats:italic>genus.</jats:p>