Self-Assembly of Stimuli-Responsive Biohybrid Synthetic-b-Recombinant Block Copolypeptides

The synthesis and original thermoresponsive behavior of hybrid diblock copolypeptides composed of synthetic and recombinant polypeptides are herein reported. A thermoresponsive recombinant elastin-like polypeptide was used as a macroinitiator to synthesize a range of poly(L-glutamic acid)-block-elastin-like polypeptide (PGlu-b-ELP) diblock copolypeptides with variable PGlu block lengths. Their temperature-triggered self-assembly in water and in phosphate-buffered saline (PBS) was investigated at the macroscopic scale using complementary techniques such as turbidimetry, dynamic and static light scattering, small-angle neutron scattering, and at the molecular scale by H-1 NMR and circular dichroism (CD). In deionized water, PGlu-b-ELP copolypeptides showed one transition from free soluble chains below the transition temperature (T-t) of the ELP block to macroscopic aggregates above the T-t. In contrast, in PBS, four successive regimes were observed upon increasing temperature: below the T-t, copolypeptides were soluble, above the T-t, large aggregates appeared and fell apart into discrete and defined spherical nanoparticles at a temperature named critical micellization temperature (CMT), before finally reaching an equilibrium. During the last regime, neutron scattering experiments revealed that the micelle-like structures underwent a densification step and expelled water from their core. In addition, H-1 NMR and CD experiments revealed, in deionized water, the formation of type II beta-turns into the ELP block upon temperature increase. These beta-turns are known to participate in the intrinsic thermoresponsive behavior of the ELPs. In contrast, in PBS, circular dichroism measurements showed an attenuation of folded structure during the self-assembly phase, leading to less cohesive aggregates able to reorganize into nanoparticles at the CMT.