Template-Assisted Enzymatic Synthesis of Oligopeptides from a Polylactide Chain

Peptides are often attached to polymer materials,as bioactive components, for the control of interactions betweenthe material and its surrounding proteins and cells. However,synthesizing peptides and attaching them to polymers can bechallenging and laborious. Herein, we describe the grafting ofoligopeptides to an aliphatic polyester, using a one-step chemoenzymaticsynthesis with papain as the biocatalyst. To enableenzyme-mediated functionalization of the polyester, ethyl hept-6-enoylalaninate (grafter) was synthesized and attached topolylactide chains using thiol−ene click reactions. The oligopeptideswere grafted onto the polylactide chains using two differentsynthetic routes: the grafting from strategy, in which the grafterwas attached to the polyester prior to oligopeptide synthesis, orthe grafting to strategy, in which oligopeptides were synthesized on the grafter first, then attached to the polymer chain. The finalproducts were analyzed and their structures were confirmed using nuclear magnetic resonance (NMR). The peptide attachmentwas evaluated using size exclusion chromatography (SEC), contact angle measurement and energy-dispersive X-ray spectroscopyscanningelectron microscopy (EDS-SEM). Furthermore, the mechanistic aspects of the synthesis of the oligopeptides on thegrafter were studied using molecular dynamics (MD) simulations. The simulation revealed that hydrogen bonding (between theP1 amide nitrogen of the grafter backbone and the carbonyl oxygen of D158 in the papain) maintain the grafter in a productiveconformation to stabilize the transition state of nitrogen inversion, a key step of the biocatalytic mechanism. Apart from beingbiologically relevant, both experimental and computational results suggest that the designed grafter is a good template forinitiating chemo-enzymatic synthesis. The results also showed that the grafting to strategy was more successful compared to thegrafting from strategy. Overall, a successful synthesis of predefined peptide functionalized polylactide was prepared, where theoligopeptides were grafted in an easy, time efficient, and environmentally friendly way.