Endo-M is one of the enzymes called endo-β-N-acetylglucosaminidases (endo-β-GlcNAc-ases). This enzyme was found by Yamamoto et al., in the culture fluid of Mucor hiemalis isolated from soil.¹⁾ Endo-M hydrolyzes N,N'-diacetylchitobiose moiety in oligosaccharides bound to the asparaginyl residue of various glycoproteins through N-glycosidic linkage. The efficacy of this enzyme comes from the fact that one N-acetylglucosamine residue remains bound to the protein while cleaving the N,N'-diacetylchitobiose moiety. The enzyme is thus able to transfer the intact oligosaccharide to suitable acceptors (Fig.1).

Haneda et al. have transferred oligosaccharides to 9-fluorenylmethoxycarbonyl-asparaginyl-N-acetylglucosaminide [Fmoc-Asn(GlcNAc)] by incubating sialotransferrin glycopeptide, asialotransferrin glycopeptide and Man₆GlcNAc₂-Asn-peptide with Endo-M.²⁾ Furthermore, synthetic hCG (β12-16)-GlcNAc-peptide has been subjected to transglycosylate of sialo complex type oligosaccharide. An alternative synthetic method of peptide containing GlcNAc has been developed by Inazu et al.³⁾ This method uses Fmoc-Asn(GlcNAc), which is synthesized from N-Fmoc aspartic acid (Fmoc-Asn-OH) and azide of GlcNAc, instead of Fmoc-Asn-OH, and it is applied to a mixed acid anhydride method using dimethylphosphothioic acid (Mpt-MA) which generally shows poor responses toward hydroxyl group. By combining this method with Endo-M, many glycopeptides can be designed and easily prepared. Yamamoto has compiled the outline of this methodology as the Chemo-Enzymatic Synthesis in his review.⁴⁾ Endo-M can also be used to create new functions, by introducing oligosaccharides, to the substances that originally do not have the oligosaccharide.⁵⁾
Unlike the conventional endo-β-GlcNAc-ase, it has been found that Endo-M is an enzyme with a broad substrate specificity, cleaving not only the high-mannose type and hybrid type of asparagine-linked oligosaccharides but also the complex type oligosaccharides in glycoproteins. Especially, the transglycosylation reaction of sialo complex type oligosaccharides was possible only by using Endo-M. Therefore, Endo-M is expected to be applied to various fields.

This Endo-M was merchandised as the fruition of NEDO project under licenses from patent-holding companies of Takara Bio Inc. and Kirin Brewery Co., LTD.