Elastin-like polypeptides (ELPs) can undergo reversible phase transitions when the temperature is increased. The primary structure of ELPs was inspired by elastin and silk peptide biopolymeric motifs. ELPs are composed of the repeating unit (Val-Pro-Gly-XAA-Gly)L. The thermodynamic phase transitions are dependent on the inserted amino acid (XAA) and the number of repeating units (L). The property of reversible transitions could promote applications as tunable elastic biomaterials for drug delivery and therapeutic applications. We used an N-terminal spin-labeling (SL) technique for two ELP monoblock and two ELP diblocks with different N-terminal hydrophobicity to attach a free radical on each of the N-terminal ends of I48 (XAA=ILE, L=48, hydrophobic block) and S96 (XAA=SER, L=96, hydrophilic block), and two diblocks I48S48 and S48I48. Electron paramagnetic resonance (EPR) method was used to probe the rotational motions of the spin-labels. We have hence correlate the internal dynamics with the coacervation of the ELPs. Our findings provided insightful information about the dynamic regimes associated with ELP phase transitions. Model of first-order kinetics was proposed and the associated energy barriers in each regime was calculated based on the Arrhenius activation energy model. The results were supported by semi-empirical quantum mechanical calculations to confirm the reliability of the observed energy barriers via the SL EPR mthod. As anticipated, the energy barriers were observed to be much higher for the hydrophobic cores than the hydrophilic corona, suggesting strong peptide interactions. At higher temperatures, the corona exhibited more considerable energy barriers also suggest an increased order of inter-peptide interactions. This study thereby provides complementary information for light optical density experiments, which provide information of phase transition, but little about peptide-interactions and inter-peptide dynamics.

Five distinct coacervation regimes of elastin-like polypeptides by dynamics of N-terminal spin label ELP dynamics via spin labeling

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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