Elasticity and Inverse Temperature Transition in Elastin

Collagen-targeted protein nanomicelles for the imaging of non-alcoholic steatohepatitis

In vivo molecular imaging tools hold immense potential to drive transformative breakthroughs by enabling researchers to visualize cellular and molecular interactions in real-time and/or at high resolution. These advancements will facilitate a deeper understanding of fundamental biological processes and their dysregulation in disease states. Here, we develop and characterize a self-assembling protein nanomicelle called collagen type I binding - thermoresponsive assembled protein (Col1-TRAP) that binds tightly to type I collagen in vitro with nanomolar affinity. For ex vivo visualization, Col1-TRAP is labeled with a near-infrared fluorescent dye (NIR-Col1-TRAP). Both Col1-TRAP and NIR-Col1-TRAP display approximately a 3.8-fold greater binding to type I collagen compared to TRAP when measured by surface plasmon resonance (SPR). We present a proof-of-concept study using NIR-Col1-TRAP to detect fibrotic type I collagen deposition ex vivo in the livers of mice with non-alcoholic steatohepatitis (NASH). We show that NIR-Col1-TRAP demonstrates significantly decreased plasma recirculation time as well as increased liver accumulation in the NASH mice compared to mice without disease over 4 hours. As a result, NIR-Col1-TRAP shows potential as an imaging probe for NASH with in vivo targeting performance after injection in mice. STATEMENT OF SIGNIFICANCE: Direct molecular imaging of fibrosis in NASH patients enables the diagnosis and monitoring of disease progression with greater specificity and resolution than do elastography-based methods or blood tests. In addition, protein-based imaging probes are more advantageous than alternatives due to their biodegradability and scalable biosynthesis. With the aid of computational modeling, we have designed a self-assembled protein micelle that binds to fibrillar and monomeric collagen in vitro. After the protein was labeled with near-infrared fluorescent dye, we injected the compound into mice fed on a NASH diet. NIR-Col1-TRAP clears from the serum faster in these mice compared to control mice, and accumulates significantly more in fibrotic livers.This work advances the development of targeted protein probes for in vivo fibrosis imaging.

Backscattering silicon spectrometer (BASIS): sixteen years in advanced materials characterization

Quasielastic neutron scattering (QENS) is an experimental technique that can measure parameters of mobility, such as diffusion jump rate and jump length, as well as localized relaxations of chemical species (molecules, ions, and segments) at atomic and nanometer length scales. Due to the high penetrative power of neutrons and their sensitivity to neutron scattering cross-section of chemical species, QENS can effectively probe mobility inside most bulk materials. This review focuses on QENS experiments performed using a neutron backscattering silicon spectrometer (BASIS) to explore the dynamics in various materials and understand their structure-property relationship. BASIS is a time-of-flight near-backscattering inverted geometry spectrometer with very high energy resolution (approximately 0.0035 meV of full width at half maximum), allowing measurements of dynamics on nano to picosecond timescales. The science areas studied with BASIS are diverse, with a focus on soft matter topics, including traditional biological and polymer science experiments, as well as measurements of fluids ranging from simple hydrocarbons and aqueous solutions to relatively complex room-temperature ionic liquids and deep-eutectic solvents, either in the bulk state or confined. Additionally, hydrogen confined in various materials is routinely measured on BASIS. Other topics successfully investigated at BASIS include quantum fluids, spin glasses, and magnetism. BASIS has been in the user program since 2007 at the Spallation Neutron Source of the Oak Ridge National Laboratory, an Office of Science User Facility supported by the U.S. Department of Energy. Over the past sixteen years, BASIS has contributed to various scientific disciplines, exploring the structure and dynamics of many chemical species and their fabrication for practical applications. A comprehensive review of BASIS contributions and capabilities would be an asset to the materials science community, providing insights into employing the neutron backscattering technique for advanced materials characterization.

Glucose-induced structural changes and anomalous diffusion of elastin

Elastin is the principal protein component of elastic fiber, which renders essential elasticity to connective tissues and organs. Here, we adopted a multi-technique approach to study the transport, viscoelastic, and structural properties of elastin exposed to various glucose concentrations (X=[gluc]/[elastin]). Laser light scattering experiments revealed an anomalous behavior (anomaly exponent, β <0.6) of elastin. In this regime (β <0.6), the diffusion constant decreases by 40% in the presence of glucose (X> 10), which suggests the structural change in elastin. We have observed a peculiar inverse temperature transition of elastin protein, which is a measure of structural change, at 40 °C through rheology experiments. Moreover, we observe its shift towards lower temperature with a higher X. FTIR revealed that the presence of glucose (X < 10) favors the formation of β-sheet structure in elastin. However, for X > 10, dominative crowding effect reduces the mobility of protein and favors the increase in β-turns and γ-turns by 25 ± 1% over the β-sheet (β-sheet decreases by 12 ± 0.8%) and α-helix (α-helix decreases by 13 ± 0.8%). The stiffness of protein is estimated through Flory characteristic ratio, C_∞ and found to be increasing with X. These glucose-based structural changes in the elastin may explain the role of glucose in age-related issues of the skin.

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).

Elastin-like Peptide in Confinement: FT-IR and NMR T 1 Relaxation Data

We employed FT-IR and NMR experiments to investigate the influence of a cell-mimicking crowding environment on the structure and dynamics of an elastin-like peptide (ELP) with the sequence GVG(VPGVG)3, which – due to a high number of hydrophobic amino acid side chains – exhibits an inverse temperature transition (ITT). As simplified crowding agent, we used 30 wt% Ficoll. The FT-IR data revealed the well-known broad ITT above ~25°C, as observed by the decrease of the relative population of random coil structures and the concomitant increase of type II β-turns. Interestingly, the addition of Ficoll leads to a destabilizing effect of type II β-turn structures. This is in contrast to the expected excluded-volume effect of the macromolecular crowder, but can be explained by weak interactions of the peptide with the polysaccharide chains of the crowding agent. Further, the crowding agent leads to the onset of a reversal of the folding transition at high temperatures. The full assignment of the ELP allowed for a residue-specific investigation of the dynamic behavior of ELP by NMR. Due to a strong change of microscopic viscosity between native/buffered conditions and crowded conditions, relaxation data remain inconclusive with respect to the observation of an ITT. Hence, no quantitative details in terms of internal conformational changes can be obtained. However, temperature dependent differences in the 13C relaxation behavior between core and terminal parts of the peptide indicate temperature induced changes in the internal dynamics with generally higher internal mobility at chain ends: This is in full agreement with FT-IR data. In harmony with the FT-IR analysis, macromolecular crowding does not lead to significant changes in the relaxation behavior.

The liquid structure of elastin

The protein elastin imparts extensibility, elastic recoil, and resilience to tissues including arterial walls, skin, lung alveoli, and the uterus. Elastin and elastin-like peptides are hydrophobic, disordered, and undergo liquid-liquid phase separation upon self-assembly. Despite extensive study, the structure of elastin remains controversial. We use molecular dynamics simulations on a massive scale to elucidate the structural ensemble of aggregated elastin-like peptides. Consistent with the entropic nature of elastic recoil, the aggregated state is stabilized by the hydrophobic effect. However, self-assembly does not entail formation of a hydrophobic core. The polypeptide backbone forms transient, sparse hydrogen-bonded turns and remains significantly hydrated even as self-assembly triples the extent of non-polar side chain contacts. Individual chains in the assembly approach a maximally-disordered, melt-like state which may be called the liquid state of proteins. These findings resolve long-standing controversies regarding elastin structure and function and afford insight into the phase separation of disordered proteins.

Bio-inspired intelligent evaporation modulation in a thermo-sensitive nanogel colloid solution for self-thermoregulation

Intelligent evaporation and temperature modulation plays an important role in self-regulation of living organisms and many industrial applications. Here we demonstrate that a poly(N-isopropylacrylamide) (PNIPAM) nanogel colloid solution can spontaneously and intelligently modulate its evaporation rate with temperature variation, which has a larger evaporation rate than distilled water at a temperature higher than its lower critical solution temperature (LCST) and a smaller evaporation rate at a temperature lower than its LCST. It performs just like human skin. Theoretical analysis based on the thermodynamic derivation reveals that the evaporation rate transition around the LCST may originate from the saturated vapor pressure transition caused by the status transformation of the PNIPAM additives. An intelligent thermoregulation system based on the PNIPAM colloid solution is also demonstrated, illustrating its potential for intelligent temperature control and acting as an artificial skin.

Hydrophobic hydration and anomalous diffusion of elastin in an ethanolic solution

Pictorial depiction of solvation of elastin molecule in aqueous and ethanol solutions. Polymer chain collapse in water and swelling in binary solvent.

Description of Hydration Water in Protein (Green Fluorescent Protein) Solution

The structurally and dynamically perturbed hydration shells that surround proteins and biomolecules have a substantial influence upon their function and stability. This makes the extent and degree of water perturbation of practical interest for general biological study and industrial formulation. We present an experimental description of the dynamical perturbation of hydration water around green fluorescent protein in solution. Less than two shells (∼5.5 Å) were perturbed, with dynamics a factor of 2-10 times slower than bulk water, depending on their distance from the protein surface and the probe length of the measurement. This dependence on probe length demonstrates that hydration water undergoes subdiffusive motions (τ ∝ q^-2.5 for the first hydration shell, τ ∝ q^-2.3 for perturbed water in the second shell), an important difference with neat water, which demonstrates diffusive behavior (τ ∝ q^-2). These results help clarify the seemingly conflicting range of values reported for hydration water retardation as a logical consequence of the different length scales probed by the analytical techniques used.

Strain-dependent fractional molecular diffusion in humid spider silk fibres

Spider silk is a material well known for its outstanding mechanical properties, combining elasticity and tensile strength. The molecular mobility within the silk's polymer structure on the nanometre length scale importantly contributes to these macroscopic properties. We have therefore investigated the ensemble-averaged single-particle self-dynamics of the prevailing hydrogen atoms in humid spider dragline silk fibres on picosecond time scales in situ as a function of an externally applied tensile strain. We find that the molecular diffusion in the amorphous fraction of the oriented fibres can be described by a generalized fractional diffusion coefficient Kα that is independent of the observation length scale in the probed range from approximately 0.3-3.5 nm. Kα increases towards a diffusion coefficient of the classical Fickian type with increasing tensile strain consistent with an increasing loss of memory or entropy in the polymer matrix.