1 research outputs found
Methyleneation of Peptides by <i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>‑Tetramethylethylenediamine (TEMED) under Conditions Used for Free Radical Polymerization: A Mechanistic Study
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 <i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>-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<sup>2</sup> and LC–MS<sup>3</sup> 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 <i>in situ</i> polymerization
systems. The use of an alternative catalyst such as sodium bisulfite
may preserve the chemical integrity of peptides during in situ polymerization