Stabilization of globular proteins via introduction of temperature-activated elastin-based switches

The coexistence region in the Van der Waals fluid and the liquid-liquid phase transitions

Cellular membraneless organelles are thought to be droplets formed within the two-phase region corresponding to proteinaceous systems endowed with the liquid-liquid transition. However, their metastability requires an additional constraint-they arise in a certain region of density and temperature between the spinodal and binodal lines. Here, we consider the well-studied van der Waals fluid as a test model to work out criteria to determine the location of the spinodal line for situations in which the equation of state is not known. Our molecular dynamics studies indicate that this task can be accomplished by considering the specific heat, the surface tension and characteristics of the molecular clusters, such as the number of component chains and radius of gyration.

Elastin-like polypeptide-based micelles as a promising platform in nanomedicine

New and improved nanomaterials are constantly being developed for biomedical purposes. Nanomaterials based on elastin-like polypeptides (ELPs) have increasingly shown potential over the past two decades. These polymers are artificial proteins of which the design is based on human tropoelastin. Due to this similarity, ELP-based nanomaterials are biodegradable and therefore well suited to drug delivery. The assembly of ELP molecules into nanoparticles spontaneously occurs at temperatures above a transition temperature (T_t). The ELP sequence influences both the T_t and the physicochemical properties of the assembled nanomaterial. Nanoparticles with desired properties can hence be designed by choosing the appropriate sequence. A promising class of ELP nanoparticles are micelles assembled from amphiphilic ELP diblock copolymers. Such micelles are generally uniform and well defined. Furthermore, site-specific attachment of cargo to the hydrophobic block results in micelles with the cargo shielded inside their core, while conjugation to the hydrophilic block causes the cargo to reside in the corona where it is available for interactions. Such control over particle design is one of the main contributing factors for the potential of ELP-based micelles as a drug delivery system. Additionally, the micelles are easily loaded with protein or peptide-based cargo by expressing it as a fusion protein. Small molecule drugs and other cargo types can be either covalently conjugated to ELP domains or physically entrapped inside the micelle core. This review aims to give an overview of ELP-based micelles and their applications in nanomedicine.

Fabrication and Characterization of Recombinant Silk-Elastin-Like-Protein (SELP) Fiber

Silk-elastin-like-protein polymers (SELPs) are genetically engineered recombinant protein sequences consisting of repeating units of silk-like and elastin-like blocks. By combining these entities, it is shown that both the characteristic strength of silk and the temperature-dependent responsiveness of elastin can be leveraged to create an enhanced stimuli-responsive material. It is hypothesized that SELP behavior can be influenced by varying the silk-to-elastin ratio. If the responsiveness of the material at different ratios is significantly different, this would allow for the design of materials with specific temperature-based swelling and mechanical properties. This study demonstrates that SELP fiber properties can be controlled via a temperature transition dependent on the ratio of silk-to-elastin in the material. SELP fibers are experimentally wet spun from polymers with different ratios of silk-to-elastin and conditioned in either a below or above transition temperature (T t ) water bath prior to characterization. The fibers with higher elastin content showed more stimuli-responsive behavior compared to the fibers with lower elastin content in the hot (57-60 °C) versus cold (4-7 °C) environment, both computationally and experimentally. This work builds a foundation for developing SELP materials with well-characterized mechanical properties and responsive features.

Cardiomyocyte intracellular cholesteryl ester accumulation promotes tropoelastin physical alteration and degradation: Role of LRP1 and cathepsin S

Dyslipemia has a direct impact on cardiac remodeling by altering extracellular matrix (ECM) components. One of the main ECM components is elastin, a proteic three-dimensional network that can be efficiently degraded by cysteine proteases or cathepsins. Dyslipemic status in insulin resistance and combined hyperlipoproteinemia diseases include raised levels of very low density lipoproteins (VLDL), triglyceride (TG)-cholesteryl ester (CE)-rich lipoproteins. Enhanced VLDL concentration promotes cardiomyocyte intracellular cholesteryl ester (CE) accumulation in a LRP1-dependent manner. The aim of this work was to analyze the effect of cardiomyocyte intracellular CE accumulation on tropoelastin (TE) characteristics and to investigate the role of LRP1 and cathepsin S (CatS) on these effects. Molecular studies showed that LRP1 deficiency impaired CE selective uptake and accumulation from TG-CE-rich lipoproteins (VLDL+IDL) and CE-rich lipoproteins (aggregated LDL, agLDL). Biochemical and confocal microscopic studies showed that LRP1-mediated intracellular CE accumulation increased CatS mature protein levels and induced an altered intracellular TE globule structure. Biophysical studies evidenced that LRP1-mediated intracellular CE accumulation caused a significant drop of Tg2 glass transition temperature of cardiomyocyte secreted TE. Moreover, CatS deficiency prevented the alterations in TE intracellular globule structure and on TE glass transition temperature. These results demonstrate that LRP1-mediated cardiomyocyte intracellular CE accumulation alters the structural and physical characteristics of secreted TE through an increase in CatS mature protein levels. Therefore, the modulation of LRP1-mediated intracellular CE accumulation in cardiomyocytes could impact pathological ventricular remodeling associated with insulin-resistance and combined hyperlipoproteinemia, pathologies characterized by enhanced concentrations of TG-CE-rich lipoproteins.

Lipid loading of human vascular smooth muscle cells induces changes in tropoelastin protein levels and physical structure

Aggregated low-density lipoprotein (agLDL), one of the main LDL modifications in the arterial intima, contributes to massive intracellular cholesteryl ester (CE) accumulation in human vascular smooth muscle cells (VSMC), which are major producers of elastin in the vascular wall. Our aim was to analyze the levels, physical structure, and molecular mobility of tropoelastin produced by agLDL-loaded human VSMC (agLDL-VSMC) versus that produced by control VSMC. Western blot analysis demonstrated that agLDL reduced VSMC-tropoelastin protein levels by increasing its degradation rate. Moreover, our results demonstrated increased levels of precursor and mature forms of cathepsin S in agLDL-VSMC. Fourier transform infrared analysis revealed modifications in the secondary structures of tropoelastin produced by lipid-loaded VSMCs. Thermal and dielectric analyses showed that agLDL-VSMC tropoelastin has decreased glass transition temperatures and distinct chain dynamics that, in addition to a loss of thermal stability, lead to strong changes in its mechanical properties. In conclusion, agLDL lipid loading of human vascular cells leads to an increase in cathepsin S production concomitantly with a decrease in cellular tropoelastin protein levels and dramatic changes in secreted tropoelastin physical structure. Therefore, VSMC-lipid loading likely determines alterations in the mechanical properties of the vascular wall and plays a crucial role in elastin loss during atherosclerosis.

Laser-induced transepidermal elimination of dermal content by fractional photothermolysis

The wound healing process in skin is studied in human subjects treated with fractional photothermolysis. In-vivo histological evaluation of vacuoles formed over microthermal zones (MTZs) and their content is undertaken. A 30-W, 1550-nm single-mode fiber laser system delivers an array of 60 microm or 140 microm 1e2 incidence microbeam spot size at variable pulse energy and density. Treatments span from 6 to 20 mJ with skin excisions performed 1-day post-treatment. Staining with hematoxylin and eosin demonstrates an intact stratum corneum with vacuolar formation within the epidermis. The re-epithelialization process with repopulation of melanocytes and keratinocytes at the basal layer is apparent by 1-day post-treatment. The dermal-epidermal (DE) junction is weakened and separated just above zones of dermal coagulation. Complete loss of dermal cell viability is noted within the confines of the MTZs 1-day post-treatment, as assessed by lactate dehydrogenase. All cells falling outside the irradiation field remain viable. Content within the epidermal vacuoles stain positively with Gomori trichrome, suggesting a dermal origin. However, the positive staining could be due to loss of specificity after thermal alteration. Nevertheless, this dermal extrusion hypothesis is supported by very specific positive staining with an antihuman elastin antibody. Fractional photothermolysis creates microthermal lesions that allow transport and extrusion of dermal content through a compromised DE junction. Some dermal material is incorporated into the microepidermal necrotic debris and shuttled up the epidermis to eventually be exfoliated through the stratum corneum. This is the first report of a nonablative laser-induced transport mechanism by which dermal content can be predictably extruded biologically through the epidermis. Thus, treatment with the 1550-nm fiber laser may provide the first therapeutic option for clinical indications, including pigmentary disorders such as medically recalcitrant melasma, solar elastosis, as well as depositional diseases such as mucinosis and amyloidosis.

Temperature-dependent conformational transitions and hydrogen-bond dynamics of the elastin-like octapeptide GVG(VPGVG): a molecular-dynamics study

A joint experimental/theoretical investigation of the elastin-like octapeptide GVG(VPGVG) was carried out. In this article a comprehensive molecular-dynamics study of the temperature-dependent folding and unfolding of the octapeptide is presented. The current study, as well as its experimental counterpart (see companion article in this issue) find that this peptide undergoes an inverse temperature transition (ITT), leading to a folding at approximately 40-60 degrees C. In addition, an unfolding transition is identified at unusually high temperatures approaching the normal boiling point of water. Due to the small size of the system, two broad temperature regimes are found: the ITT regime at approximately 10-60 degrees C and the unfolding regime at approximately T > 60 degrees C, where the peptide has a maximum probability of being folded at T approximately 60 degrees C. A detailed molecular picture involving a thermodynamic order parameter, or reaction coordinate, for this process is presented along with a time-correlation function analysis of the hydrogen-bond dynamics within the peptide as well as between the peptide and solvating water molecules. Correlation with experimental evidence and ramifications on the properties of elastin are discussed.