Solid-phase Synthesis of C-mannosylated Glycopeptide on WSXWS Motif of Human Erythropoietin Receptor

Protein C-mannosylation is a widely conserved posttranslational modification in multicellular organisms although the function of this modification is yet to be clarified. To evaluate the effect of this modification, a C-mannosyltryptophan containing glycopeptide of human erythropoietin receptor (EPOR), which includes WSXWS motif conserved in cytokine receptor superfamily, was synthesized by microwave assisted solid-phase synthesis using per-O-benzyl protected amino acids and C-mannosyltryptophan on Sieber amide resin. Comparative NMR analysis of the C-mannosyl glycopeptide and a corresponding naked peptide revealed that the C-mannosylation enhances the NOE signal between the peptide main chain and the aromatic side chain to suggest enhancement of conformational stability of the WSXWS motif and its surrounding regions.