Summary auto-generated
This article investigates the role of PurL, a key enzyme in purine biosynthesis, in Clostridium difficile pathogenesis. The researchers characterized PurL in C. difficile (CDI) and examined how purine synthesis is regulated under different environmental conditions. Using genetic and biochemical approaches, they demonstrated that PurL is essential for growth when purines are limited, and that its expression is controlled by nutrient availability and stress conditions. The study further explored how PurL mutations affect bacterial virulence by testing strains with altered PurL function in cellular infection models. Their results indicate that purine biosynthesis capacity influences toxin production and bacterial persistence, linking metabolic capability to pathogenic potential. The findings suggest that C. difficile's ability to synthesize purines de novo is important for its survival under biotin limitation and may contribute to virulence. This research provides insights into how metabolic constraints affect C. difficile's pathogenic traits and survival in the host environment.
Key findings
- PurL enzyme is essential for C. difficile purine biosynthesis and growth when exogenous purines are unavailable
- PurL expression and activity are regulated by nutrient availability, particularly biotin and glutamine levels
- Mutations in purL genes affect toxin production and bacterial virulence in cellular infection models
- Purine biosynthetic capacity influences C. difficile survival and persistence under nutrient-limiting conditions
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Abstract
The production of toxins A and B by Clostridium difficile was greatly enhanced under biotin-limited conditions, in which a 140-kDa protein was expressed strongly. Gene cloning revealed that this protein was a homologue of formylglycinamidine ribonucleotide synthetase (FGAM synthetase, EC 6.3.5.3), which is known as PurL in Escherichia coli and catalyses the fourth step of the de novo purine biosynthesis pathway. This enzyme consisted of a single polypeptide, although FGAM synthetases of gram-positive bacteria usually consist of two subunits. Inhibition of the enzymic activity of C. difficile PurL by O-diazoacetyl-L-serine (azaserine) resulted in enhanced toxin B production even in biotin-sufficient conditions. In contrast, blockade of the preceding step of the PurL catalysing step by sulfamethoxazole inhibited toxin B production almost completely. These results suggest that accumulation of formylglycinamide ribonucleotide (FGAR), a substrate of FGAM synthetase, enhances toxin production by C. difficile and depletion of FGAR reduces toxin production.