Chemoenzymatic synthesis of polypeptides containing the unnatural amino acid 2-aminoisobutyric acid

Abstract

Polypeptides containing 2-aminoisobutyric acid (Aib) units as an unnatural amino acid residue were synthesized by papain-catalyzed chemoenzymatic polymerization of a tripeptide ethyl ester l-Ala-Aib-l-Ala-OEt in an aqueous medium. The Aib-containing polypeptide adopted an α-helix conformation in both the solid and solution phases, which was induced by the periodic Aib residue.

Periodic introduction of aromatic units in polypeptides via chemoenzymatic polymerization to yield specific secondary structures with high thermal stability

“…Chemoenzymatic synthesis of polypeptides containing aromatic residues Unnatural amino acids are generally unfavorable substrates for chemoenzymatic polymerization using proteases due to their substrate specificity. Indeed, no polymer was obtained for the papain-catalyzed polymerization of the aromatic amino acid monomer 4-aminobenzoic acid ethyl ester (Abz-OEt), resulting in approximately complete recovery of the monomer, as observed in the case of other unnatural amino acids such as 2-aminoisobutyric acid and nylon esters (Scheme 1) [21,27]. To overcome the poor specificity of the Abz unit to papain, we modified the Abz unit with Gly or Ala at both termini to obtain tripeptide ethyl esters via a solution-based condensation method.…”

“…Recently, we demonstrated that the poor affinity of unnatural amino acids to proteases can be mitigated by modification with natural amino acids in chemoenzymatic polymerization. A tripeptide ester consisting of 2-aminoisobutyric acid (Aib) between two alanine residues was efficiently polymerized in the presence of papain, whereas the chemoenzymatic polymerization of Aib ester did not proceed because of low affinity to papain [27,28]. The resulting polypeptide with an Aib-containing periodic sequence transitioned to an α-helix secondary structure, driven by the helix-inducing Aib units.…”

Chemoenzymatic Synthesis of Polypeptides for Use as Functional and Structural Materials

“…Methyl [79] Alkaline d-peptidase (2-4) [79] Aib b) Ethyl [123] Papain (4-5) [123] 3-Aminopropionic acid Methyl, [73,124] ethyl [73,124] Papain (6-9) [73,124] 4-Aminobutyric acid Methyl, [73,124] ethyl [73,124] Papain (5-9) [73,124] 6-Aminohexanoic acid Methyl [73,124] Papain (6-9) [73,124] a) Values in parentheses show the range of average degree of polymerization (DP) obtained using the proteases; b) Polymerization was conducted using a tripeptide ester containing an Aib unit.…”

“…Aib-containing polypeptides were enzymatically synthesized by utilizing a tripeptide ester containing an Aib unit in the middle of the triad sequence. [123] Sandwiching the Aib unit with l-alanine residues, which are good substrates for papain, resulted in the efficient recognition of the substrate by papain and allowed the polymerization of the tripeptide ester to proceed. The resulting polypeptide, poly(AlaAibAla), assumed a helical conformation in both solid and solution states, as confirmed by IR and circular dichroism analyses.…”

“…2017, 17, 1700177 Figure 9. Polypeptides that assume unnatural structures: A) star-shaped polypeptides, [44,70] B) telechelic polypeptides, [55,117] C) polypeptides containing Aib as an unnatural amino acid, [123] and D) polypeptides containing nylon units. [73,124] www.advancedsciencenews.com www.mbs-journal.de with papain, although several proteases, such as bromelain, proteinase K, and lipase, were tested.…”