Optimization of the enzymatic synthesis of O-glycan core 2 structure by use of a genetic algorithm

Enzyme catalysed tandem reactions

To transfer to the laboratory, the excellent efficiency shown by enzymes in Nature, biocatalysis, had to mimic several synthetic strategies used by the living organisms. Biosynthetic pathways are examples of tandem catalysis and may be assimilated in the biocatalysis field for the use of isolated multi-enzyme systems in the homogeneous phase. The concurrent action of several enzymes that work sequentially presents extraordinary advantages from the synthetic point of view, since it permits a reversible process to become irreversible, to shift the equilibrium reaction in such a way that enantiopure compounds can be obtained from prochiral or racemic substrates, reduce or eliminate problems due to product inhibition or prevent the shortage of substrates by dilution or degradation in the bulk media, etc. In this review we want to illustrate the developments of recent studies involving in vitro multi-enzyme reactions for the synthesis of different classes of organic compounds.

Synthesis and modifications of carbohydrates, using biotransformations

Enzymes continue to be used as important catalysts, for the generation of rare and 'unnatural' monosaccharides and for the selective formation of glycosidic linkages. Multi-enzyme systems have been employed in one-pot strategies for multistep reaction sequences and for co-factor regeneration. The efficiency of glycosidases for glycosylation reactions has been dramatically increased by active-site mutagenesis to generate glycosynthases. First reports have detailed the expansion and optimization of glycosynthase substrate specificity by directed evolution. Novel glycosyltransferases are being identified from genomic databases and have been shown to glycosylate complex metabolites, such as glycopeptide antibiotics, with exquisite selectivity and in good yields. An emerging field is the application of glycosynthases and glycosyltransferases to reactions on solid support, generating potential applications in microarrays.

Enzymatic synthesis of the core-2 sialyl Lewis X O-glycan on the tumor-associated MUC1a' peptide

Starting from a tumor-associated synthetic MUC1-derived peptide MUC1a' and using a completely enzymatic approach for the synthesis of the core-2 sialyl Lewis X glycopart, the following glycopeptide was synthesized: AHGV[Neu5Ac(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc(alpha1-O)]TSAPDTR. First, polypeptide N-acetylgalactosaminyltransferase 3 was used to site-specifically glycosylate MUC1a' to give MUC1a'-GalNAc. Then, in a one-pot reaction employing beta-galactosidase and core-2 beta6-N-acetylglucosaminyltransferase the core-2 O-glycan structure was prepared. The core-2 structure was then sequentially galactosylated, sialylated, and fucosylated by making use of beta4-galactosyltransferase 1, alpha3-sialyltransferase 3, and alpha3-fucosyltransferase 3, respectively, resulting in the sialyl Lewis X glycopeptide. The overall yield of the final compound was 23% (3.2 mg, 1.4 micromol). During the synthesis three intermediate glycopeptides containing O-linked GalNAc, Gal(beta1-4)GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc, and Neu5Ac(alpha2-3)Gal(beta1-4)GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc, respectively, were isolated in mg quantities. All products were characterized by mass spectrometry and NMR spectroscopy.