Conformational Control of UDP-Galactopyranose Mutase Inhibition

Association between clinical-biological characteristics of Klebsiella pneumoniae and 28-day mortality in patients with bloodstream infection

BACKGROUND

Klebsiella pneumoniae bloodstream infection (KP BSI) is a severe clinical condition characterized by high mortality rates. Despite the clinical significance, accurate predictors of mortality in KP BSI have yet to be fully identified.

METHODS

A retrospective analysis was conducted on the clinical data of 90 cases of KP BSI. The clinical data was extracted from electronic medical records. Antimicrobial susceptibility testing, string testing, and whole-genome sequencing (WGS) were performed on all isolates. Additionally, relevant bioinformatics analyses, such as phylogenetic analysis and assessment of resistance and virulence genes, were carried out. Logistic regression modeling was employed to evaluate the risk factors associated with 28-day mortality in patients with KP BSI, considering both host characteristics and the characteristics of the causative Klebsiella pneumoniae (KP) isolates.

RESULTS

Among the 90 patients included in this study, the 28-day mortality rate for those with KP BSI was 30.00% (27/90). Multivariate analysis revealed several host-related factors associated with an increased risk of 28-day mortality. These factors included an elevated qSOFA score (odds ratio [OR] 2.98, 95% confidence interval [CI] 1.21-7.31, p = 0.017), presence of septic shock (OR 8.21, 95% CI 1.63-41.93, p = 0.008), and nosocomial infection (OR 7.72, 95% CI 1.71-34.74, p = 0.002). Regarding bacterial factors, the presence of the virulence genes rfbA/B/D (OR 8.53, 95% CI 1.41-51.57, p = 0.020) was identified as an independent risk factor, particularly for nosocomial infection patients. However, hypermucoviscosity phenotype, ST type, serotype, and resistance genes were not associated with an increased risk of 28-day mortality.

CONCLUSION

The carriage of virulence genes rfbA/B/D, which is responsible for the synthesis of O-antigen, was associated with poor prognosis of KP BSI. It may facilitate the clinical management of patients with bloodstream infection (BSI) caused by hypervirulent KP strains, especially those with rfbA/B/D genes.

CLINICAL TRIAL NUMBER

Not applicable.

Steric Control of the Rate-Limiting Step of UDP-Galactopyranose Mutase

Galactose is an abundant monosaccharide found exclusively in mammals as galactopyranose (Gal p), the six-membered ring form of this sugar. In contrast, galactose appears in many pathogenic microorganisms as the five-membered ring form, galactofuranose (Gal f). Gal f biosynthesis begins with the conversion of UDP-Gal p to UDP-Gal f catalyzed by the flavoenzyme UDP-galactopyranose mutase (UGM). Because UGM is essential for the survival and proliferation of several pathogens, there is interest in understanding the catalytic mechanism to aid inhibitor development. Herein, we have used kinetic measurements and molecular dynamics simulations to explore the features of UGM that control the rate-limiting step (RLS). We show that UGM from the pathogenic fungus Aspergillus fumigatus also catalyzes the isomerization of UDP-arabinopyranose (UDP-Ara p), which differs from UDP-Gal p by lacking a -CH₂-OH substituent at the C5 position of the hexose ring. Unexpectedly, the RLS changed from a chemical step for the natural substrate to product release with UDP-Ara p. This result implicated residues that contact the -CH₂-OH of UDP-Gal p in controlling the mechanistic path. The mutation of one of these residues, Trp315, to Ala changed the RLS of the natural substrate to product release, similar to the wild-type enzyme with UDP-Ara p. Molecular dynamics simulations suggest that steric complementarity in the Michaelis complex is responsible for this distinct behavior. These results provide new insight into the UGM mechanism and, more generally, how steric factors in the enzyme active site control the free energy barriers along the reaction path.