The structural characteristics of synthetically glycosylated tau protein sequences

The microtubule‐associated protein tau is the primary constituent of neurofibrillary tangles, a pathological hallmark of Alzheimer's Disease. In its diseased state, tau is phosphorylated on over 30 residues, many of which are alternatively modified by O‐linked glycosylation by N‐acetylglucosamine (O‐GlcNAc) in tau's native state. We hypothesized that glycosylation of threonine and serine residues on tau peptides may induce a structural effect different from that of phosphorylation at these locations. We have employed a scheme for the synthesis of glycopeptides incorporating O‐GlcNAc and isolated the amino acid building block, Fmoc‐Thr(β‐D‐pGlcNAc)‐OH. Furthermore, we have developed a functional group to mimic O‐GlcNAc modification (pseudo‐glycosylation). Peptides from the tau proline‐rich domain were synthesized and the conformations were characterized using circular dichroism and NMR for the unmodified, phosphorylated, pseudo‐glycosylated, and glycosylated peptides. Phosphorylated sequences exhibited high propensity to form a type II polyproline helix. In contrast, glycosylated peptides exhibited alternative structures. These findings suggest a structural role for tau modification by O‐GlcNAc. This project was supported by the Howard Hughes Medical Institute and the Alzheimer's Association.