4-O-Acetyl-sialic acid (Neu4,5Ac2) in acidic milk oligosaccharides of the platypus (Ornithorhynchus anatinus) and its evolutionary significance

Tadasu Urashima, Hiroaki Inamori, Kenji Fukuda, Tadao Saito, Michael Messer, Olav T. Oftedal

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Monotremes (echidnas and platypus) retain an ancestral form of reproduction: egg-laying followed by secretion of milk onto skin and hair in a mammary patch, in the absence of nipples. Offspring are highly immature at hatching and depend on oligosaccharide-rich milk for many months. The primary saccharide in long-beaked echidna milk is an acidic trisaccharide Neu4,5Ac2(α2-3)Gal(β1-4)Glc (4-O-acetyl 3′-sialyllactose), but acidic oligosaccharides have not been characterized in platypus milk. In this study, acidic oligosaccharides purified from the carbohydrate fraction of platypus milk were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 1H-nuclear magnetic resonance spectroscopy. All identified structures, except Neu5Ac(α2-3)Gal(β1-4)Glc (3′-sialyllactose) contained Neu4,5Ac2 (4-O-acetyl-sialic acid). These include the trisaccharide 4-O-acetyl 3′-sialyllactose, the pentasaccharide Neu4,5Ac2(α2-3)Gal(β1-4)GlcNAc(β1-3)Gal(β1-4)Glc (4-O-acetyl-3′-sialyllacto-N-tetraose d) and the hexasaccharide Neu4,5Ac2(α2-3)Gal(β1-4)[Fuc(α1-3)]GlcNAc(β1-3)Gal(β1-4)Glc (4-O-acetyl-3′-sialyllacto-N-fucopentaose III). At least seven different octa- to deca-oligosaccharides each contained a lacto-N-neohexaose core (LNnH) and one or two Neu4,5Ac2 and one to three fucose residues. We conclude that platypus milk contains a diverse (≥20) array of neutral and acidic oligosaccharides based primarily on lactose, lacto-N-neotetraose (LNnT) and LNnH structural cores and shares with echidna milk the unique feature that all identified acidic oligosaccharides (other than 3′-sialyllactose) contain the 4-O-acetyl-sialic acid moiety. We propose that 4-O-acetylation of sialic acid moieties protects acidic milk oligosaccharides secreted onto integumental surfaces from bacterial hydrolysis via steric interference with bacterial sialidases. This may be of evolutionary significance since taxa ancestral to monotremes and other mammals are thought to have secreted milk, or a milk-like fluid containing oligosaccharides, onto skin surfaces.

Original languageEnglish
Pages (from-to)683-697
Number of pages15
Issue number6
Publication statusPublished - 2014 Dec 12


  • evolution
  • milk oligosaccharides
  • monotreme
  • platypus
  • sialic acid

ASJC Scopus subject areas

  • Biochemistry


Dive into the research topics of '4-O-Acetyl-sialic acid (Neu4,5Ac2) in acidic milk oligosaccharides of the platypus (Ornithorhynchus anatinus) and its evolutionary significance'. Together they form a unique fingerprint.

Cite this