Impact of aromatic residues on the intrinsic disorder and transitional behaviour of model IDPs.

Understanding the interplay between order and disorder in intrinsically disorder proteins (IDPs), and its impact on the properties and features of materials manufactured from them, is a major challenge in the design of protein-based synthetic polymers intended for advanced functions. In this paper an elastin-like diblock co-recombinamer amphiphile (Phe-ELR) based on a hydrophobic block containing five phenylalanine (Phe) residues proximal to the carboxyl function of a glutamic acid (Glu) residue upon folding, and with Glu as the guest residue in the hydrophilic part, was engineered and its assembly behaviour compared with another amphiphilic ELR used as control. Phe-ELR was tailored in order to clarify the impact of the presence of aromatic residues in the amino acid sequence, which even in early studies by Urry's group already demonstrated a certain out-of-trend behaviour compared with other apolar amino acids, especially non-aromatic ones, on ELR behaviour. The combination of several experimental techniques indicates strong molecular interactions associated with the Phe residue, thus resulting in limited reversible character of the temperature-induced transitions during sequential thermal cycles, a lower than expected transition enthalpy, and clear differences in its supramolecular assembly with respect to the control ELR. A distinctive pre-aggregated state for the Phe-ELR under any condition of pH and temperature is found. Eventually, this state gives rise to Phe-core micelles or a solid jelly-like material, depending on the concentration, pH and presence of salts. In conclusion, it appears that the presence of aromatic residues and their ability to promote strong inter- and intramolecular interactions at any temperature and pH causes a complete modification of the order-disorder interplay present in other, non-aromatic ELRs. These molecular events have a profound impact on the physical properties of the resulting polymer when compared with other ELRs. This work helps to shed light on the limits that govern intrinsic disorder in ELRs beyond its inverse temperature transition.

Self-assembly in elastin-like recombinamers: a mechanism to mimic natural complexity.

The topic of self-assembled structures based on elastin-like recombinamers (ELRs, i.e., elastin-like polymers recombinantly bio-produced) has released a noticeable amount of references in the last few years. Most of them are intended for biomedical applications. In this review, a complete revision of the bibliography is carried out. Initially, the self-assembly (SA) concept is considered from a general point of view, and then ELRs are described and characterized based on their intrinsic disorder. A classification of the different self-assembled ELR-based structures is proposed based on their morphologies, paying special attention to their tentative modeling. The impact of the mechanism of SA on these biomaterials is analyzed. Finally, the implications of ELR SA in biological systems are considered.