Characterization and mutational analysis of two UDP-galactose 4-epimerases in Streptococcus pneumoniae TIGR4

• Published in: Biochemistry (Moscow) Vol. 83; no. 1; pp. 37 - 44
• Main Authors: Chen, L. L., Han, D. L., Zhai, Y. F., Wang, J. H., Wang, Y. F., Chen, M.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-01-2018; Springer; Springer Nature B.V
• Subjects: Analysis; Bacteria; Bacterial pneumonia; Biochemistry; Biomedical and Life Sciences; Biomedicine; Bioorganic Chemistry; Cellulose; Chemical properties; Dextrose; Enzymes; Epimerase; Galactose; Gene mutation; Genetic aspects; Glucose; Health aspects; Identification and classification; Life Sciences; Metabolism; Microbiology; N-Acetylgalactosamine; N-Acetylglucosamine; Observations; Physiological aspects; Pneumonia; Serotypes; Streptococcus infections; Streptococcus pneumoniae; Substitutes; Substrate specificity; Substrates; Vaccines; Virulence; Virulence (Microbiology); Virulence factors; mutation; TIGR4; substrate specificity; UDP-galactose 4-epimerase (GalE)
• ISSN: 0006-2979; 1608-3040
• DOI: 10.1134/S0006297918010054

Current clinical treatments for pneumococcal infections have many limitations and are faced with many challenges. New capsular polysaccharide structures must be explored to cope with diseases caused by different serotypes of
Streptococcus pneumoniae
. UDP-galactose 4-epimerase (GalE) is an essential enzyme involved in polysaccharide synthesis. It is an important virulence factor in many bacterial pathogens. In this study, we found that two genes (
galE
sp1
and
galE
sp2
) are responsible for galactose metabolism in pathogenic S.
pneumoniae
TIGR4. Both GalE
Sp1
and Gal
ESp2
were shown to catalyze the epimerization of UDP-glucose (UDP-Glc)/UDP-galactose (UDP-Gal), but only GalE
Sp2
was shown to catalyze the epimerization of UDP-N-acetylglucosamine (UDP-GlcNAc)/UDP-N-acetylgalactosamine (UDP-GalNAc). Interestingly, GalE
Sp2
had 3-fold higher epimerase activity toward UDP-Glc/UDP-Gal than GalE
Sp1
. The biochemical properties of GalE
Sp2
were studied. GalE
Sp2
was stable over a wide range of temperatures, between 30 and 70°C, at pH 8.0. The K86G substitution caused GalE
Sp2
to lose its epimerase activity toward UDP-Glc and UDP-Gal; however, substitution C300Y in GalE
Sp2
resulted in only decreased activity toward UDP-GlcNAc and UDP-GalNAc. These results indicate that the Lys86 residue plays a critical role in the activity and substrate specificity of GalE
Sp2
.