Abstract
BackgroundSialylated glycoconjugates play important roles in physiological and pathological processes. However, available sialylated oligosaccharides source is limited which is a barrier to study their biological roles. This work reports an efficient approach to produce sialic acid-modified lactuloses and investigates their inhibitory effects on Staphylococcus aureus (S. aureus).MethodsA one-pot two-enzyme (OPTE) sialylation system was used to efficiently synthesize sialylated lactuloses. Silica gel flash chromatography column was employed to purify the sialylated products. The purity and identity of the product structures were confirmed with mass spectrometry (MS) and nuclear magnetic resonance (NMR). The inhibitory effect of sialylated lactuloses against S. aureus was evaluated by using microplate assay, fluorescence microscopy, DAPI (4',6-diamidino-2-phenylindole) fluorescence staining and protein leakage quantification.ResultsNeu5Ac-containing sialylated lactuloses with either α2,3- or α2,6-linkages were efficiently synthesized via an efficient OPTE sialylation system using α-2,3-sialyltransferase or α-2,6-sialyltransferase, respectively. Neu5Ac-α2,3-lactulose and Neu5Ac-α2,6-lactulose significantly inhibited the growth of S. aureus. Fluorescence microscopy and DAPI fluorescence staining indicated that the sialylated lactuloses might disrupt nucleic acid synthesis of S. aureus.ConclusionsNeu5Ac-containing sialylated lactuloses had higher antibacterial activity against S. aureus than non-sialylated lactulose. The inhibitory effect of Neu5Ac-α2,3-lactulose was superior to that of Neu5Ac-α2,6-lactulose. The sialylated lactuloses might inhibit S. aureus by causing cell membrane leakage and disrupting nucleic acid synthesis.
Highlights
Lactulose [4-O-(β-D-galactopyranosyl)-D-fructose] is a non-natural disaccharide and is synthesized from lactose by isomerization under alkaline conditions [1] or using cellobiose 2-epimerase [2]
Neu5Ac-containing sialylated lactuloses with either α2,3- or α2,6-linkages were efficiently synthesized via an efficient one-pot two-enzyme (OPTE) sialylation system using α-2,3-sialyltransferase or α-2,6sialyltransferase, respectively
Fluorescence microscopy and DAPI fluorescence staining indicated that the sialylated lactuloses might disrupt nucleic acid synthesis of S. aureus
Summary
Lactulose [4-O-(β-D-galactopyranosyl)-D-fructose] is a non-natural disaccharide and is synthesized from lactose by isomerization under alkaline conditions [1] or using cellobiose 2-epimerase [2]. Lactulose can be produced in the presence of fructose via β-galactosidase bioconversion [1, 3,4]. Sialic acids are a family of α-keto acids with a nine-carbon backbone. They are usually present as terminal carbohydrate units of glycoproteins and glycolipids of vertebrates, components of capsular polysaccharides, and lipooligosaccharides of pathogenic bacteria [7]. Sialylated glycoconjugates play the important roles in physiological and pathological processes, including cellular recognition, bacterial infection, viral infection, and tumor cell metastasis, development and differentiation [8]. Sialylated glycoconjugates play important roles in physiological and pathological processes. This work reports an efficient approach to produce sialic acid-modified lactuloses and investigates their inhibitory effects on Staphylococcus aureus (S. aureus)
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