Peptide self-cleavage at a canaline residue: application to a solubilizing tag system for native chemical ligation
Canaline (Can) is a non-proteinogenic amino acid containing an aminooxy group in its side chain. Can-containing peptides can be synthesized by standard Fmoc SPPS using Fmoc-Can(2-Cl-Trt). Here, for the first time, a Can residue within a peptide sequence was found to spontaneously cleave the main chain amide bond under slightly acidic conditions (pH 4–5). Contrastingly, Can-containing peptides are completely stable under the acidic conditions for HPLC purification (pH ca. 2) and under the neutral conditions for native chemical ligation (NCL). Taking advantage of these unique pH-dependent properties of Can, a novel solubilizing tag system for NCL-mediated protein synthesis using (Lys/Arg)n-Can was developed.