Synthesis of neoglycoproteins using oligosaccharide-transfer activity with endo-beta-N-acetylglucosaminidase

We describe a novel method for the enzymatic synthesis of neoglycoproteins. Endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) had high levels of transglycosylation activity. The enzyme activity of Endo-A was markedly increased by adding 4-L-aspartyl-glycosylamine (GlcNAc-Asn) to the reaction mixture. Digesting (Man)6(GlcNAc)2 with the enzyme in the presence of GlcNAc-Asn gave a mixture of hydrolytic ((Man)6GlcNAc) and transglycosylic ((Man)6(GlcNAc)2-Asn) products. By means of transglycosylation, (Man)6GlcNAc was transferred en bloc to the partially deglycosylated ovalbumin glycopeptide (EEKYN(GlcNAc)LTSVL) concomitant with the hydrolysis of (Man)6-GlcNAc)2Asn. The structure of the transglycosylation product was designated as (Man)6(GlcNAc)2-peptide by amino acid composition and sequence analysis as well as ion mass spectrometry. The enzyme also transferred oligosaccharide to partially deglycosylated ribonuclease B (GlcNAc-protein) during the hydrolysis of (Man)6-(GlcNAc)2Asn. Native ribonuclease B had (Man)5-9 (GlcNAc)2 as its heterogeneous N-linked sugar chains. High performance liquid chromatography showed that all of the N-linked sugar chains of the synthetic neoribonuclease of the pyridylamino derivatives were modified to (Man)6(GlcNAc)2.