The Internal Structural Dynamics of Elastin-Like Polypeptide Assemblies by 13C-Direct Detected NMR Spectroscopy

Elastin-like polypeptides (ELPs) are biocompatible polymers exhibiting lower critical solution temperature (LCST) behavior, making them valuable in various applications, including drug delivery and tissue engineering. This study addresses the atomistic-level understanding of ELP self-assembly, focusing on their internal structural dynamics. Conventional proton-detected nuclear magnetic resonance (NMR) spectroscopy faces limitations in studying ELP aggregates due to accelerated proton exchange processes, which cause significant resonance broadening. Herein, we show how to overcome this hurdle by using carbon-13-detected NMR. This method mitigates issues related to amide proton exchange, allowing for a residue-resolved view of the internal configuration of ELP aggregates. With this method, we record residue-resolved 15N relaxation rates, revealing three features. (i) Proline residues within the PGXGV pentapeptide repeats (X being any amino acid except proline) of ELP become motional restricted upon aggregation, indicating their role as interchain contacts. (ii) Pentapeptides with alanine guest residue X display particularly significantly reduced motional freedom upon aggregation. (iii) Even within large ELP aggregates, fast internal dynamics characterize the peptide chains in a way that is reminiscent of condensed liquid phases. The presented study is the first proof of concept that 13C-direct detection is a viable tool to delineate the internal structural dynamics of condensed ELP phases by NMR. It might, thus, help to foster new investigations of their aggregation mechanisms.

Elastin-Like Peptide as a Model for Disordered Proteins: Diffusion Behaviour in Self-Crowding Conditions

Despite the current high interest, there is limited information on diffusion data for intrinsically disordered proteins (IDPs). This study investigates the effect of crowding on the diffusion behaviour of an elastin-like peptide (ELP), by combined pulse field gradient (PFG) and static field gradient (SFG) NMR techniques. We interpret our findings in terms of highly dynamic chain assemblies with weak interactions, resulting in ELP diffusion that is primarily governed by the viscous flow of the solvent. The diffusion behaviour of the peptide appears to resemble that of globular proteins rather than flexible linear polymers over a wide concentration range.

Structural and Dynamical Properties of Elastin-Like Peptides near Their Lower Critical Solution Temperature

Elastin-like peptides (ELPs) are artificially derived intrinsically disordered proteins (IDPs) mimicking the hydrophobic repeat unit in the protein elastin. ELPs are characterized by a lower critical solution temperature (LCST) in aqueous media. Here, we investigate the sequence GVG(VPGVG)₃ over a wide range of temperatures (below, around, and above the LCST) and peptide concentrations employing all-atom molecular dynamics simulations, where we focus on the role of intra- and interpeptide interactions. We begin by investigating the structural properties of a single peptide that demonstrates a hydrophobic collapse with temperature, albeit moderate, because the sequence length is short. We observe a change in the interaction between two peptides from repulsive to attractive with temperature by evaluating the potential of mean force, indicating an LCST-like behavior. Next, we explore dynamical and structural properties of peptides in multichain systems. We report the formation of dynamical aggregates with coil-like conformation, in which valine central residues play an important role. Moreover, the lifetime of contacts between chains strongly depends on the temperature and can be described by a power-law decay that is consistent with the LCST-like behavior. Finally, the peptide translational and internal motion are slowed by an increase in the peptide concentration and temperature.

Confinement Effects on Glass-Forming Aqueous Dimethyl Sulfoxide Solutions

Combining broadband dielectric spectroscopy and nuclear magnetic resonance studies, we analyze the reorientation dynamics and the translational diffusion associated with the glassy slowdown of the eutectic aqueous dimethyl sulfoxide solution in nano-sized confinements, explicitly, in silica pores with different diameters and in ficoll and lysozyme matrices at different concentrations. We observe that both rotational and diffusive dynamics are slower and more heterogeneous in the confinements than in the bulk but the degree of these effects depends on the properties of the confinement and differs for the components of the solution. For the hard and the soft matrices, the slowdown and the heterogeneity become more prominent when the size of the confinement is reduced. In addition, the dynamics are more retarded for dimethyl sulfoxide than for water, implying specific guest-host interactions. Moreover, we find that the temperature dependence of the reorientation dynamics and of the translational diffusion differs in severe confinements, indicating a breakdown of the Stokes-Einstein-Debye relation. It is discussed to what extent these confinement effects can be rationalized in the framework of core-shell models, which assume bulk-like and slowed-down motions in central and interfacial confinement regions, respectively.

Temperature induced conformational changes in the elastin-like peptide GVG(VPGVG)3

Elastin-like peptides are biopolymers that display LCST behaviour in solution quite similar to other synthetic polymers like polyethylene oxide. Here we study the structure of the peptide GVG(VPGVG)3 in a temperature range of 25 °C to 70 °C with small angle neutron scattering. The LCST for this peptide is outside the experimental range of temperatures. Molecular conformation is well described within the model of a random coil but increasing temperature leads to significant changes. The peptide displays a combination of conformational change and aggregation that show up in the scattering at low and intermediate scattering vector q. The aggregate size is determined from an integral measure of the scattered intensity. It increases with temperature and concentration. For low concentration we find a size variation with temperature that may be related to the collapse of conformation at the inverse temperature transition (ITT).

Molecular Dynamics Simulations of Water, Silica, and Aqueous Mixtures in Bulk and Confinement

Aqueous systems are omnipresent in nature and technology. They show complex behaviors, which often originate in the existence of hydrogen-bond networks. Prominent examples are the anomalies of water and the non-ideal behaviors of aqueous solutions. The phenomenology becomes even richer when aqueous liquids are subject to confinement. To this day, many properties of water and its mixtures, in particular, under confinement, are not understood. In recent years, molecular dynamics simulations developed into a powerful tool to improve our knowledge in this field. Here, our simulation results for water and aqueous mixtures in the bulk and in various confinements are reviewed and some new simulation data are added to improve our knowledge about the role of interfaces. Moreover, findings for water are compared with results for silica, exploiting that both systems form tetrahedral networks.

Properties of Hydrogen-Bonded Liquids at Interfaces

Effects of interfaces on hydrogen-bonded liquids play major roles in nature and technology. Despite their importance, a fundamental understanding of these effects is still lacking. In large parts, this shortcoming is due to the high complexity of these systems, leading to an interference of various interactions and effects. Therefore, it is advisable to take gradual approaches, which start from well designed and defined model systems and systematically increase the level of intricacy towards more complex mimetics. Moreover, it is necessary to combine insights from a multitude of methods, in particular, to link novel preparation strategies and comprehensive experimental characterization with inventive computational and theoretical modeling. Such concerted approach was taken by a group of preparative, experimentally, and theoretically working scientists in the framework of Research Unit FOR 1583 funded by the Deutsche Forschungsgemeinschaft (German Research Foundation). This special issue summarizes the outcome of this collaborative research. In this introductory article, we give an overview of the covered topics and the main results of the whole consortium. The following contributions are review articles or original works of individual research projects.