Polyproline tetramer organizing peptides in fetal bovine serum acetylcholinesterase

► Polyproline peptides are present in fetal bovine serum acetylcholinesterase. ► We isolated five types of polyproline peptide. ► One type was composed solely of prolines, 13 to 25 residues in length. ► Four types included a single non-proline terminal residue. ► The serum acetylcholinesterase tetramer is organized around a polyproline peptide.