Enzymatic synthesis of poly(α-ethyl β-aspartate) by poly(ethylene glycol) modified poly(aspartate) hydrolase-1

We recently discovered that poly(aspartate) (PAA) hydrolase-1 from Pedobacter sp. KP-2 has a unique property of specifically cleaving the amide bond between β-aspartate units in thermally synthesized PAA (tPAA). In the present study, the enzymatic synthesis of poly(α-ethyl β-aspartate) (β-PAA) was performed by taking advantage of the substrate specificity of PAA hydrolase-1. No polymerization of diethyl L-aspartate by native PAA hydrolase-1 occurred because of the low dispersibility of the enzyme in organic solvent. Poly(ethylene glycol) (PEG) modification of the enzyme improved its dispersibility and enabled it to polymerize the monomer substrate. MALDI-TOF MS analysis showed that the synthesized polymer was observed in the range of m/z = 750-2 500. This analysis also revealed that the polymer was composed of ethyl aspartate units, containing either an ethyl ester or a free carboxyl end group at its carboxyl terminus. (1) H NMR analysis demonstrated that the synthesized polymer consisted of only β-amide linkages. Thus, the present results indicate that PAA hydrolase-1 modified with PEG is useful for the synthesis of β-PAA due to its unique substrate specificity and good dispersibility in organic solvent.