Nanomechanical properties of SSTSAA microcrystals are dominated by the inter-sheet packing.

Amyloid fibrils have been associated with human disease for many decades, but it has also become apparent that they play a functional, non-disease-related role in e.g. bacteria and mammals. Moreover, they have been shown to possess interesting mechanical properties that can be harnessed for future man-made applications. Here, the mechanical behaviour of SSTSAA microcrystals has been investigated. The SSTSAA peptide organization in these microcrystals has been related to that in the corresponding amyloid fibrils. Using high-pressure X-ray diffraction experiments, the bulk modulus K, which is the reciprocal of the compressibility ß, has been calculated to be 2.48 GPa. This indicates that the fibrils are tightly packed, although the packing of most native globular proteins is even better. It is shown that the value of the bulk modulus is mainly determined by the compression along the c-axis, that relates to the inter-sheet distance in the fibrils. These findings corroborate earlier data obtained by AFM and molecular dynamics simulations that showed that mechanical resistance varies according to the direction of the applied strain, which can be related to packing and hydrogen bond contributions. Pressure experiments provide complementary information to these techniques and help to acquire a full mechanical characterization of biomolecular assemblies. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

The Right-Handed Parallel ß-Helix Topology of Erwinia chrysanthemi Pectin Methylesterase Is Intimately Associated with Both Sequential Folding and Resistance to High Pressure.

The complex topologies of large multi-domain globular proteins make the study of their folding and assembly particularly demanding. It is often characterized by complex kinetics and undesired side reactions, such as aggregation. The structural simplicity of tandem-repeat proteins, which are characterized by the repetition of a basic structural motif and are stabilized exclusively by sequentially localized contacts, has provided opportunities for dissecting their folding landscapes. In this study, we focus on the Erwinia chrysanthemi pectin methylesterase (342 residues), an all-ß pectinolytic enzyme with a right-handed parallel ß-helix structure. Chemicals and pressure were chosen as denaturants and a variety of optical techniques were used in conjunction with stopped-flow equipment to investigate the folding mechanism of the enzyme at 25 °C. Under equilibrium conditions, both chemical- and pressure-induced unfolding show two-state transitions, with average conformational stability (ΔG° = 35 ± 5 kJ·mol-1) but exceptionally high resistance to pressure (Pm = 800 ± 7 MPa). Stopped-flow kinetic experiments revealed a very rapid (τ < 1 ms) hydrophobic collapse accompanied by the formation of an extended secondary structure but did not reveal stable tertiary contacts. This is followed by three distinct cooperative phases and the significant population of two intermediate species. The kinetics followed by intrinsic fluorescence shows a lag phase, strongly indicating that these intermediates are productive species on a sequential folding pathway, for which we propose a plausible model. These combined data demonstrate that even a large repeat protein can fold in a highly cooperative manner.

In Vivo Water Dynamics in Shewanella oneidensis Bacteria at High Pressure.

Following observations of survival of microbes and other life forms in deep subsurface environments it is necessary to understand their biological functioning under high pressure conditions. Key aspects of biochemical reactions and transport processes within cells are determined by the intracellular water dynamics. We studied water diffusion and rotational relaxation in live Shewanella oneidensis bacteria at pressures up to 500 MPa using quasi-elastic neutron scattering (QENS). The intracellular diffusion exhibits a significantly greater slowdown (by -10-30%) and an increase in rotational relaxation times (+10-40%) compared with water dynamics in the aqueous solutions used to resuspend the bacterial samples. Those results indicate both a pressure-induced viscosity increase and slowdown in ionic/macromolecular transport properties within the cells affecting the rates of metabolic and other biological processes. Our new data support emerging models for intracellular organisation with nanoscale water channels threading between macromolecular regions within a dynamically organized structure rather than a homogenous gel-like cytoplasm.

HIF-1α metabolically controls collagen synthesis and modification in chondrocytes.

Endochondral ossification, an important process in vertebrate bone formation, is highly dependent on correct functioning of growth plate chondrocytes1. Proliferation of these cells determines longitudinal bone growth and the matrix deposited provides a scaffold for future bone formation. However, these two energy-dependent anabolic processes occur in an avascular environment1,2. In addition, the centre of the expanding growth plate becomes hypoxic, and local activation of the hypoxia-inducible transcription factor HIF-1α is necessary for chondrocyte survival by unidentified cell-intrinsic mechanisms3-6. It is unknown whether there is a requirement for restriction of HIF-1α signalling in the other regions of the growth plate and whether chondrocyte metabolism controls cell function. Here we show that prolonged HIF-1α signalling in chondrocytes leads to skeletal dysplasia by interfering with cellular bioenergetics and biosynthesis. Decreased glucose oxidation results in an energy deficit, which limits proliferation, activates the unfolded protein response and reduces collagen synthesis. However, enhanced glutamine flux increases α-ketoglutarate levels, which in turn increases proline and lysine hydroxylation on collagen. This metabolically regulated collagen modification renders the cartilaginous matrix more resistant to protease-mediated degradation and thereby increases bone mass. Thus, inappropriate HIF-1α signalling results in skeletal dysplasia caused by collagen overmodification, an effect that may also contribute to other diseases involving the extracellular matrix such as cancer and fibrosis.

Insects as an Alternative Source for the Production of Fats for Cosmetics.

Insects may provide an environmentally friendly way of producing high-quality bio-based materials that can be implemented for cosmetic applications. Insects can be bred on organic waste, in high numbers, and on small surfaces, therefore, making large scale industrial breeding possible. Fats from three insect species: the black soldier fly (BSF) (Hermetia illucens), the locust (Locusta migratoria), and the house cricket (Acheta domesticus) were evaluated for potential use in skin care. Insects were dried and fats were extracted using petroleum ether. The fats were further refined, and the fatty acid composition and the acid value were determined. The fats were used in a hand cream formulation and compared with the currently used mink-and plant-derived oils. Fatty acid analysis indicates that BSF contains > 60% of lauric acid, which makes it less suitable for application in a skin-care product, whereas locust and cricket fats are rich in C16 and C18 fatty acids which makes them more suitable. Phospholipids and free fatty acid levels in the three insect species are relatively high compared with commercial, refined oils, and need to be removed by appropriate refining protocols. Odor and color also need to be removed by physical refinement to improve the applicability.

Pressure as a Limiting Factor for Life.

Facts concerning the stability and functioning of key biomolecular components suggest that cellular life should no longer be viable above a few thousand atmospheres (200-300 MPa). However, organisms are seen to survive in the laboratory to much higher pressures, extending into the GPa or even tens of GPa ranges. This is causing main questions to be posed concerning the survival mechanisms of simple to complex organisms. Understanding the ultimate pressure survival of organisms is critical for food sterilization and agricultural products conservation technologies. On Earth the deep biosphere is limited in its extent by geothermal gradients but if life forms exist in cooler habitats elsewhere then survival to greater depths must be considered. The extent of pressure resistance and survival appears to vary greatly with the timescale of the exposure. For example, shock experiments on nanosecond timescales reveal greatly enhanced survival rates extending to higher pressure. Some organisms could survive bolide impacts thus allowing successful transport between planetary bodies. We summarize some of the main questions raised by recent results and their implications for the survival of life under extreme compression conditions and its possible extent in the laboratory and throughout the universe.

Water Dynamics in Shewanella oneidensis at Ambient and High Pressure using Quasi-Elastic Neutron Scattering.

Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and relaxation dynamics at pico- to nanosecond timescales and at length scales relevant to cellular dimensions. Studies of high pressure dynamic effects in live organisms are needed to understand Earth's deep biosphere and biotechnology applications. Here we applied QENS to study water transport in Shewanella oneidensis at ambient (0.1 MPa) and high (200 MPa) pressure using H/D isotopic contrast experiments for normal and perdeuterated bacteria and buffer solutions to distinguish intracellular and transmembrane processes. The results indicate that intracellular water dynamics are comparable with bulk diffusion rates in aqueous fluids at ambient conditions but a significant reduction occurs in high pressure mobility. We interpret this as due to enhanced interactions with macromolecules in the nanoconfined environment. Overall diffusion rates across the cell envelope also occur at similar rates but unexpected narrowing of the QENS signal appears between momentum transfer values Q = 0.7-1.1 Å(-1) corresponding to real space dimensions of 6-9 Å. The relaxation time increase can be explained by correlated dynamics of molecules passing through Aquaporin water transport complexes located within the inner or outer membrane structures.

Laboratory investigation of high pressure survival in Shewanella oneidensis MR-1 into the gigapascal pressure range.

The survival of Shewanella oneidensis MR-1 at up to 1500 MPa was investigated by laboratory studies involving exposure to high pressure followed by evaluation of survivors as the number (N) of colony forming units (CFU) that could be cultured following recovery to ambient conditions. Exposing the wild type (WT) bacteria to 250 MPa resulted in only a minor (0.7 log N units) drop in survival compared with the initial concentration of 10(8) cells/ml. Raising the pressure to above 500 MPa caused a large reduction in the number of viable cells observed following recovery to ambient pressure. Additional pressure increase caused a further decrease in survivability, with approximately 10(2) CFU/ml recorded following exposure to 1000 MPa (1 GPa) and 1.5 GPa. Pressurizing samples from colonies resuscitated from survivors that had been previously exposed to high pressure resulted in substantially greater survivor counts. Experiments were carried out to examine potential interactions between pressure and temperature variables in determining bacterial survival. One generation of survivors previously exposed to 1 GPa was compared with WT samples to investigate survival between 37 and 8°C. The results did not reveal any coupling between acquired high pressure resistance and temperature effects on growth.

High hydrostatic pressure: a probing tool and a necessary parameter in biophysical chemistry.

High pressures extending up to several thousands of atmospheres provide extreme conditions for biological organisms to survive. Recent studies are investigating the survival mechanisms and biological function of microorganisms under natural and laboratory conditions extending into the GigaPascal range, with applications to understanding the Earth's deep biosphere and food technology. High pressure has also emerged as a useful tool and physical parameter for probing changes in the structure and functional properties of biologically important macromolecules and polymers encountered in soft matter science. Here we highlight some areas of current interest in high pressure biophysics and physical chemistry that are emerging at the frontier of this cross-disciplinary field.

Phenoloxidase activity and thermostability of Cancer pagurus and Limulus polyphemus hemocyanin.

The intrinsic and inducible o-diphenoloxidase (o-diPO) activity of Cancer pagurus hemocyanin (CpH) and Limulus polyphemus hemocyanin (LpH) were studied using catechol, l-Dopa and dopamine as substrates. The kinetic analysis shows that dopamine is a more specific substrate for CpH than catechol and l-Dopa (K(m) value of 0.01 mM for dopamine versus 0.67 mM for catechol, and 2.14 mM for l-Dopa), while k(cat) is highest for catechol (2.44 min(-1) versus 0.67 min(-1) for l-Dopa and 0.71 min(-1) for dopamine). On treatment with 4mM sodium dodecyl sulfate (SDS) or by proteolysis the o-diPO activity of CpH increases about twofold. In contrast, native LpH shows no o-diPO activity, and exhibits only a slight activity after incubation with SDS. Neither CpH nor LpH show intrinsic mono-PO activity with l-tyrosine and tyramine as substrates. To explore the possible correlation between the degree of PO activity and protein stability of arthropod hemocyanins, the thermal stability of CpH and LpH was investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. CpH is found to be less thermostable (T(m)~80 °C), suggesting that the dicopper active sites are more accessible, thereby allowing the hemocyanin to show PO activity in the native state. The LpH, on the other hand, is more thermostable (T(m)~92 °C), suggesting the existence of a correlation between the thermal stability and the intrinsic PO activity of arthropod hemocyanins.

In-situ spectroscopic investigation of ultrasonic assisted unfolding and aggregation of insulin.

It is well-known that fibrillogenesis of proteins can be influenced by diverse external parameters, such as temperature, pressure, agitation or chemical agents. The present preliminary study suggests that ultrasonic excitation at moderate intensities has a significant influence on the unfolding and aggregation behaviour of insulin. Irradiation with an average sound intensity of even as low as 70mW/cm(2) leads to a lowering of the unfolding and aggregation temperature up to 7K. The effect could be explained by an increase of the aggregation kinetics due to ultrasonically induced acoustic micro-streaming in the insulin solution that most probably enhances the aggregation rate. The clear and remarkable effect at relatively low sound intensities offers interesting options for further applications of ultrasound in biophysics and biochemistry. On the other hand, a process that causes a change of kinetics equivalent to 7K also gives a warning signal concerning the safety of those medical ultrasonic devices that work in this intensity range.

Reversible heat inactivation of copper sites precedes thermal unfolding of molluscan (Rapana thomasiana) hemocyanin.

Hemocyanin (Hc) is a type-3 copper protein, containing dioxygen-binding active sites consisting of paired copper atoms. In the present study the thermal unfolding of the Hc from the marine mollusc Rapana thomasiana (RtH) has been investigated by combining differential scanning calorimetry, Fourier transform infrared (FTIR) and UV-vis absorption spectroscopy. Two important stages in the unfolding pathway of the Hc molecule were discerned. A first event, with nonmeasurable heat absorption, occurring around 60°C, lowers the binding of dioxygen to the type-3 copper groups. This pretransition is reversible and is ascribed to a slight change in the tertiary structure. In a second stage, with midpoint around 80°C, the protein irreversibly unfolds with a loss of secondary structure and formation of amorphous aggregates. Experiments with the monomeric structural subunits, RtH1 and RtH2, indicated that the heterogeneity in the process of thermal denaturation can be attributed to the presence of multiple 50kDa functional units with different stability. In accordance, the irreversible unfolding of a purified functional unit (RtH2-e) occurred at a single transition temperature. At slightly alkaline pH (Tris buffer) the C-terminal ß-sheet rich domain of the functional unit starts to unfold before the α-helix-rich N-terminal (copper containing) domain, triggering the collapse of the global protein structure. Even around 90°C some secondary structure is preserved as shown by the FTIR spectra of all investigated samples, confirming the high thermostability of molluscan Hc.

An X-ray and neutron scattering study of the equilibrium between trimethylamine N-oxide and urea in aqueous solution.

The interaction of the osmolytes trimethylamine N-oxide (TMAO) and urea in aqueous solutions at 40 °C was investigated by isotopic substitution neutron scattering at a TMAO mole fraction of 0.05 and TMAO/urea concentration ratios of 1 : 2 and 1 : 4. The partial pair distribution functions obtained by the empirical potential structure refinement method are consistent with those obtained previously for similar pure TMAO and 1 : 1 TMAO-urea solutions and indicate that urea progressively replaces the water molecules in the first coordination shell of the TMAO oxygen atom. The apparent association constant for the TMAO : urea complex (K(1)) was calculated to be 0.14 M(-1), which is of the same order as the experimental urea-protein binding constants per site reported in the literature. This confirms that the two osmolytes act independently at least in the physiological range.

Nanomechanical and structural properties of native cellulose under compressive stress.

Cellulose is an important biopolymer with applications ranging from its use as an additive in pharmaceutical products to the development of novel smart materials. This wide applicability arises in part from its interesting mechanical properties. Here we report on the use of high pressure X-ray diffraction and Raman spectroscopy in a diamond anvil cell to determine the bulk and local elastic moduli of native cellulose. The modulus values obtained are 20 GPa for the bulk modulus and 200-355 and 15 GPa for the crystalline parts and the overall elastic (Young's) modulus, respectively. These values are consistent with those calculated from tensile measurements. Above 8 GPa, the packing of the cellulose chains within the fibers undergoes significant structural distortion, whereas the chains themselves remain largely unaffected by compression.

Amyloid features and neuronal toxicity of mature prion fibrils are highly sensitive to high pressure.

Prion proteins (PrP) can aggregate into toxic and possibly infectious amyloid fibrils. This particular macrostructure confers on them an extreme and still unexplained stability. To provide mechanistic insights into this self-assembly process, we used high pressure as a thermodynamic tool for perturbing the structure of mature amyloid fibrils that were prepared from recombinant full-length mouse PrP. Application of high pressure led to irreversible loss of several specific amyloid features, such as thioflavin T and 8-anilino-1-naphthalene sulfonate binding, alteration of the characteristic proteinase K digestion pattern, and a significant decrease in the ß-sheet structure and cytotoxicity of amyloid fibrils. Partial disaggregation of the mature fibrils into monomeric soluble PrP was observed. The remaining amyloid fibrils underwent a change in secondary structure that led to morphologically different fibrils composed of a reduced number of proto-filaments. The kinetics of these reactions was studied by recording the pressure-induced dissociation of thioflavin T from the amyloid fibrils. Analysis of the pressure and temperature dependence of the relaxation rates revealed partly unstructured and hydrated kinetic transition states and highlighted the importance of collapsing and hydrating inter- and intramolecular cavities to overcome the high free energy barrier that stabilizes amyloid fibrils.

Rapid acquisition of Gigapascal-high-pressure resistance by Escherichia coli.

Pressure and temperature are important environmental variables that influence living systems. However, while they vary over a considerable range on Earth and other planets, it has hardly been addressed how straightforwardly and to what extent cellular life can acquire resistance to extremes of these parameters within a defined genomic context and a limited number of generations. Nevertheless, this is a very pertinent question with respect to the penetration of life in allegedly inhospitable environments. In this study, directed evolution was used to reveal the potential of the nonsporulating and mesophilic model bacterium Escherichia coli to develop the ability to survive exposure to high temperature or pressure. While heat resistance could only marginally be increased, our data show that piezoresistance could readily and reproducibly be extended into the GPa range, thereby greatly exceeding the currently recognized maximum for growth or survival.

FTIR 2D correlation spectroscopy of α1 and α2 fractions of an alkali-pretreated gelatin.

An alkali-pretreated gelatin (pI~4.9) was fractionated by means of alcohol coacervation and semi-preparative gel chromatography. The thermal responses of the isolated α fractions, the coacervate and the total gelatin were investigated by 2D-correlation FTIR spectroscopy in the amide I band region (1600-1700 cm⁻¹). The gelation temperature was the same for all examined samples (24.5°C) while the melting temperature of the α2 fraction was lower (30°C) than that of the other samples (32.5°C). The 2D COS plots indicate that on cooling (gelation) the core sequence of conformational changes is the same for all samples. On heating, however, the α2 fraction deviates from the α1-containing samples and shows an earlier disappearance of the triple helix signal in the event sequence. The lower melting temperature (less thermostable gelatin gel) of the α2 fraction thus results from a different conformational cascade of the α2 chains upon melting. In all samples the initial conformational changes take place in the ß-turns, providing further evidence for the models proposed previously.

Structural and mechanical properties of TTR105-115 amyloid fibrils from compression experiments.

Amyloid fibrils, originally associated with neurodegenerative diseases, are now recognized to have interesting mechanical properties. By using synchrotron x-ray diffraction at high pressure in a diamond anvil cell we determined the bulk modulus of TTR105-115 amyloid fibrils in water and in silicone oil to be 2.6 and 8.1 GPa, respectively. The compression characteristics of the fibrils are quite different in the two media, revealing the presence of cavities along the axis of the fibrils, but not between the ß-sheets, which are separated by a dry interface as in a steric zipper motif. Our results emphasize the importance of peptide packing in determining the structural and mechanical properties of amyloid fibrils.

Dynamics of the crystal to plastic crystal transition in the hydrogen bonded N-isopropylpropionamide.

N-Isopropylpropionamide (NiPPA), which can self-associate via hydrogen bonds, was found to undergo a solid-solid transition as identified by DSC and X-ray diffraction. Below the melting temperature of 51 °C NIPPA adopts a plastic crystalline state with a tetragonal unit cell until it transforms into an ordered crystal with a monoclinic structure at temperatures ≤10 °C. Dielectric spectroscopy was used to characterize the dynamics of the system, determining the activation parameters for the plastic to crystalline phase transition. The activation enthalpy is relatively high, as expected for a system that involves hydrogen bonds. However, most of the activation energy as the plastic phase assumes a more crystalline state is due to the activation entropy, suggesting that the increased cooperativity observed in the relaxation processes is due to a steric locking of the molecules.

Consistent picture of the reversible thermal unfolding of hen egg-white lysozyme from experiment and molecular dynamics.

Synchrotron radiation circular dichroism, Fourier transform infrared, and nuclear magnetic resonance spectroscopies, and small-angle x-ray scattering were used to monitor the reversible thermal unfolding of hen egg white lysozyme. The results were compared with crystal structures and high- and low-temperature structures derived from molecular-dynamics calculations. The results of both experimental and computational methods indicate that the unfolding process starts with the loss of ß-structures followed by the reversible loss of helix content from ∼40% at 20°C to 27% at 70°C and ∼20% at 77°C, beyond which unfolding becomes irreversible. Concomitantly there is a reversible increase in the radius of gyration of the protein from 15 Å to 18 Å. The reversible decrease in forward x-ray scattering demonstrates a lack of aggregation upon unfolding, suggesting the change is due to a larger dilation of hydration water than of bulk water. Molecular-dynamics simulations suggest a similar sequence of events and are in good agreement with the (1)H(N) chemical shift differences in nuclear magnetic resonance. This study demonstrates the power of complementary methods for elucidating unfolding/refolding processes and the nature of both the unfolded structure, for which there is no crystallographic data, and the partially unfolded forms of the protein that can lead to fibril formation and disease.