Abstract
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. Lactobacillus salivarius 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 in vivo. Some lactobacilli are heterofermentative and can metabolize pentoses, using a pathway in which transketolase and transaldolase are key enzymes. L. salivarius 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 Lactobacillus genus.
Highlights
The Gram-positive, lactic acid bacterium Lactobacillus salivarius UCC118 (Claesson et al, 2006) is of particular interest as a member of a group of probiotic bacteria (Neville & O’Toole, 2010) that successfully colonize the human gastrointestinal tract, conferring such health benefits as prevention or hindrance of intestinal infection, elimination of food-borne pathogens (Corr et al, 2007) and reduction in inflammation and food intolerance (Sheil et al, 2004)
There are a variety of donor and acceptor sugar phosphates that can be converted by transketolase, making it, along with the enzyme transaldolase, a central enzyme in the link between the pentose phosphate pathway and glycolysis (Lindqvist et al, 1992)
We present high-resolution crystal structures of the L. salivarius UCC118 Tkt protein (LsTktA) in the presence and absence of the cofactor thiamine pyrophosphate (TPP) and Mg2+ ions, which have been determined as part of a directed structural genomics approach to furthering our understanding of how these bacterial strains colonize and persist in the human gut and enhance the wellbeing of the host
Summary
The Gram-positive, lactic acid bacterium Lactobacillus salivarius UCC118 (Claesson et al, 2006) is of particular interest as a member of a group of probiotic bacteria (Neville & O’Toole, 2010) that successfully colonize the human gastrointestinal tract, conferring such health benefits as prevention or hindrance of intestinal infection, elimination of food-borne pathogens (Corr et al, 2007) and reduction in inflammation and food intolerance (Sheil et al, 2004). Megaplasmid-encoded transaldolase (LSL_1888, mipB) and transketolase (LSL_1946, tktA) complete the pentose phosphate pathway of L. salivarius UCC118. This is predicted to give it a competitive advantage when ribose, abundant in plant material, is present in the diet. In addition to its significant metabolic role, Tkt may be relevant as a catalyst for the industrial organic synthesis of pure chiral products (Nikkola et al, 1994). Both its broad substrate specificity and its ability to catalyse the formation of asymmetric C—C bonds make the Tkt enzyme an attractive biocatalyst
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