Total chemical synthesis and NMR characterization of the glycopeptide tx5a, a heavily post-translationally modified conotoxin, reveals that the glycan structure is alpha-D-Gal-(1 -> 3)-alpha-D-GalNAc

Summary, in English

The 13-amino acid glycopeptide tx5a (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* = 6-bromotryptophan and Thr* = Gal-GalNAc-threonine), isolated from Conus textile, causes hyperactivity and spasticity when injected intracerebral ventricularly into mice. It contains nine post-translationally modified residues: four cysteine residues, two gamma-carboxyglutamic acid residues, and one residue each of 6-bromotryptophan, 4-trans-hydroxyproline and glycosylated threonine. The chemical nature of each of these has been determined with the exception of the glycan linkage pattern on threonine and the stereochemistry of the 6-bromotryptophan residue. Previous investigations have demonstrated that tx5a contains a disaccharide composed of N-acetylgalactosamine (GalNAc) and galactose (Gal), but the interresidue linkage was not characterized. We hypothesized that tx5a contained the T-antigen, beta-D-Gal-(1-->3)-alpha-D-GalNAc, one of the most common O-linked glycan structures, identified previously in another Conus glycopeptide, contalukin-G. We therefore utilized the peracetylated form of this glycan attached to Fmoc-threonine in an attempted synthesis. While the result-ing synthetic peptide (Gla-Cys-Cys-Gla-Asp-Gly-Trp*-Cys-Cys-Thr*-Ala-Ala-Hyp-OH, where Trp* =6-bromotryptophan and Thr* = beta-D-Gal-(1-->3)-alpha-D-GalNAc-threonine) and the native peptide had almost identical mass spectra, a comparison of their RP-HPLC chromatograms suggested that the two forms were not identical. Two-dimensional H-1 homonuclear and C-13-H-1 heteronuclear NMR spectroscopy of native tx5a isolated from Conus textile was then used to determine that the glycan present on tx5a indeed is not the aforementioned T-antigen, but rather alpha-D-Gal-(1-->3)-alpha-D-GalNAc.

• Författare: J Kang; W Low; T Norberg; J Meisenhelder; Karin M Hansson; Johan Stenflo; GP Zhou; J Imperial; BM Olivera; AC Rigby; AG Craig
• Avdelning/ar: Klinisk kemi, Malmö
• Publiceringsår: 2004
• Språk: Engelska
• Sidor: 4939-4949
• Publikation/Tidskrift/Serie: European Journal of Biochemistry
• Volym: 271
• Issue: 23-24
• Länkar: http://dx.doi.org/10.1111/j.1432-1033.2004.04464.x
• Dokumenttyp: Artikel i tidskrift
• Förlag: Wiley-Blackwell
• Ämne: Medicinal Chemistry
• Nyckelord: Conus textile; glycopeptide synthesis
• Status: Published
• Forskningsgrupp: Clinical Chemistry, Malmö
• ISBN/ISSN/Övrigt: ISSN: 0014-2956