TAU proteins belong to the microtubule-associated protein (MAP) family and are involved in the pathogenesis of Alzheimer’s disease. In the human brain, there are six TAU isoforms ranging from 352 to 441 amino acids in length. These isoforms vary at the carboxyl terminal according to the presence of either three repeat or four repeat domains (R1-R4), in addition to the presence or absence of one or two insert domains at the amino-terminus. Tau Peptide (45-73) is a 29-amino acid long peptide derived from the Exon 2/Insert 1 domain.
Pyroglutamyl (pGlu) peptides may spontaneously form when either Glutamine (Q) or Glutamic acid (E) is located at the sequence N-terminus. The conversion of Q or E to pGlu is a natural occurrence and in general it is believed that the hydrophobic γ-lactam ring of pGlu may play a role in peptide stability against gastrointestinal proteases. Pyroglutamyl peptides are therefore considered a normal subset of such peptides and are included as part of the peptide purity during HPLC analysis.