Abstract
We previously reported that A. hydrophila GalU mutants were still able to produce UDP-glucose introduced as a glucose residue in their lipopolysaccharide core. In this study, we found the unique origin of this UDP-glucose from a branched α-glucan surface polysaccharide. This glucan, surface attached through the O-antigen ligase (WaaL), is common to the mesophilic Aeromonas strains tested. The Aeromonas glucan is produced by the action of the glycogen synthase (GlgA) and the UDP-Glc pyrophosphorylase (GlgC), the latter wrongly indicated as an ADP-Glc pyrophosphorylase in the Aeromonas genomes available. The Aeromonas glycogen synthase is able to react with UDP or ADP-glucose, which is not the case of E. coli glycogen synthase only reacting with ADP-glucose. The Aeromonas surface glucan has a role enhancing biofilm formation. Finally, for the first time to our knowledge, a clear preference on behalf of bacterial survival and pathogenesis is observed when choosing to produce one or other surface saccharide molecules to produce (lipopolysaccharide core or glucan).
Highlights
IntroductionGlucose-1-phosphate is the early precursor for glycogen synthesis, and it is first converted to ADP-glucose (ADP-Glc) in a reversible reaction catalyzed by ADP-glucose pyrophosphorylase (EC 2.7.7.27)
Mechanisms of glycogen formation have been largely studied for Escherichia coli [1]
Glucose-1-phosphate is the early precursor for glycogen synthesis, and it is first converted to ADP-glucose (ADP-Glc) in a reversible reaction catalyzed by ADP-glucose pyrophosphorylase (EC 2.7.7.27)
Summary
Glucose-1-phosphate is the early precursor for glycogen synthesis, and it is first converted to ADP-glucose (ADP-Glc) in a reversible reaction catalyzed by ADP-glucose pyrophosphorylase (EC 2.7.7.27). The glucosyl unit of ADP-Glc is transferred to the nonreducing end of an a-1,4-glucan chain by glycogen synthase (EC 2.4.1.21), and a-1,6 linkages are generated by a branching enzyme (EC 2.4.1.18). UDP-glucose (UDP-Glc) is considered to be the glucosyl donor for glycogen synthesis in mammalian cells. Either ADP-Glc or UDP-Glc can serve as glucosyl donors in eukaryotic microorganisms and Plants [2]. The biosynthesis of UDP-Glc in E. coli involves the following enzymatic reactions: 1. Through GalU, Glucose-1 phosphate + UTP R UDP-Glc + PPi. 2. Through Gal E, UDP-Glc « UDP-Gal (UDP-galactose). 3. through GalT, Glucose-1 phosphate + UDP-Gal R Galactose-1 phosphate + UDP-Glc The biosynthesis of UDP-Glc in E. coli involves the following enzymatic reactions: 1. through GalU, Glucose-1 phosphate + UTP R UDP-Glc + PPi. 2. through Gal E, UDP-Glc « UDP-Gal (UDP-galactose). 3. through GalT, Glucose-1 phosphate + UDP-Gal R Galactose-1 phosphate + UDP-Glc
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