Production of Sialic Acid Analogs in Engineered E. coli: Characterization of Amino Sugar Recycling

Abstract

This research focused on the study of the amino sugar recycling and sialic acid degradation pathway as a possible entry point for N-acyl glucosamines for the production of sialic acid analogs. Meeting this objective would allow the development of a bacterial strain capable of producing non-natural nonulosonic acids that could be used in the development of medicines, vaccines or useful compounds for the study of interactions between pathogenic organisms and their host. The first step was to understand how N-acetyl-D-glucosamine-6-phosphate deacetylase reacts to different types of substrates in order to determine its tolerance to the size of acyl groups in acyl amino sugars. This was achieved by studying the enzymatic activity in an in vitro system. We determine that the enzyme has a preference for small and slightly bulky acyl groups. Then, an in silico docking modeling and an in vivo system experiment were carried out. These experiments allowed to confirm the previous results. The second project was carried out due to the uncertainty of whether the kinase involved in the catabolic pathway would be able to phosphorylate the substrates. By quantifying residual ATP, the high specificity of N-acetyl-D-glucosamine kinase could be verified. This result led us to think about the design of an organic synthesis strategy that would allow the phosphorylation of glucosamine in carbon 6. A simple synthetic route was designed based on the protection of the two most reactive moieties of the amino sugars and the reactivity of the hydroxy group on carbon 6. However, we had problems with the purification step of the final product due to its high polarity. The next stage of this investigation was to confirm the transformation of GlcNAc into ManNAc. For this, an NMR analysis was designed that would detect the presence of both sugars in the reaction system. The epimerization of ManNAc to GlcNAc was detected successfully. Notwithstanding, the reverse reaction could not be detected. Based on the results obtained in the previous stage, we realized that an error was made in the epimerization reaction since we placed the wrong kinase because we did not take into account its substrate specificity. Finally, we tried to produce sialic acid analogs in a fermentative system using different genetic variants of Escherichia coli. Two of the expected analogs, Neu5Pr and Neu5nBu, were obtained. In addition, NagA activity towards substrates with small acyl groups was confirmed.