title: Methyleneation of peptides by N,N,N,N-tetramethylethylenediamine (TEMED) under conditions used for free radical polymerization: a mechanistic study.
abstract: Free radical polymerization is often used to prepare protein and peptide-loaded hydrogels for the design of controlled release systems and molecular imprinting materials. Peroxodisulfates (ammonium peroxodisulfates (APS) or potassium peroxodisulfates (KPS)) with N,N,N,N-tetramethylethylenediamine (TEMED) are frequently used as initiator and catalyst. However, exposure to these free radical polymerization reagents may lead to modification of the protein and peptide. In this work, we show the modification of lysine residues by ammonium peroxodisulfate (APS)/TEMED of the immunostimulant thymopentin (TP5). Parallel studies on a decapeptide and a library of 15 dipeptides were performed to reveal the mechanism of modification. LC-MS of APS/TEMED-exposed TP5 revealed a major reaction product with an increased mass (+12 Da) with respect to TP5. LC-MS(2) and LC-MS(3) were performed to obtain structural information on the modified peptide and localize the actual modification site. Interpretation of the obtained data demonstrates the formation of a methylene bridge between the lysine and arginine residue in the presence of TEMED, while replacing TEMED with a sodium bisulfite catalyst did not show this modification. Studies with the other peptides showed that the TEMED radical can induce methyleneation on peptides when lysine is next to arginine, proline, cysteine, aspargine, glutamine, histidine, tyrosine, tryptophan, and aspartic acid residues. Stability of peptides and protein needs to be considered when using APS/TEMED in in situ polymerization systems. The use of an alternative catalyst such as sodium bisulfite may preserve the chemical integrity of peptides during in situ polymerization.
authors.affiliation: Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Utrecht University , Utrecht 3584 CG, The Netherlands.
authors.forename: Mehrnoosh
authors.initials: M
authors.lastname: Shirangi
authors.forename: Javier
authors.initials: J
authors.lastname: Sastre Toraño
authors.forename: Börje
authors.initials: B
authors.lastname: Sellergren
authors.forename: Wim E
authors.initials: WE
authors.lastname: Hennink
authors.forename: Govert W
authors.initials: GW
authors.lastname: Somsen
authors.forename: Cornelus F
authors.initials: CF
authors.lastname: van Nostrum
mesh_terms: D000595:Amino Acid Sequence; D000645:Ammonium Sulfate / Q000737:chemistry; D005029:Ethylenediamines / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D008970:Molecular Weight; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry*; D058105:Polymerization; D055550:Protein Stability
chemical_list: D005029:Ethylenediamines; D005609:Free Radicals; D019151:Peptide Library; D010455:Peptides; C005798:N,N,N',N'-tetramethylethylenediamine; C031276:ammonium peroxydisulfate; D000645:Ammonium Sulfate