New insights into the protein stabilizing effects of trehalose by comparing with sucrose.

Disaccharides are well known to be efficient stabilizers of proteins, for example in the case of lyophilization or cryopreservation. However, although all disaccharides seem to exhibit bioprotective and stabilizing properties, it is clear that trehalose is generally superior compared to other disaccharides. The aim of this study was to understand this by comparing how the structural and dynamical properties of aqueous trehalose and sucrose solutions influence the protein myoglobin (Mb). The structural studies were based on neutron and X-ray diffraction in combination with empirical potential structure refinement (EPSR) modeling, whereas the dynamical studies were based on quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations. The results show that the overall differences in the structure and dynamics of the two systems are small, but nevertheless there are some important differences which may explain the superior stabilizing effects of trehalose. It was found that in both systems the protein is preferentially hydrated by water, but that this effect is more pronounced for trehalose, i.e. trehalose forms less hydrogen bonds to the protein surface than sucrose. Furthermore, the rotational motion around dihedrals between the two glucose rings of trehalose is slower than in the case of the dihedrals between the glucose and fructose rings of sucrose. This leads to a less perturbed protein structure in the case of trehalose. The observations indicate that an aqueous environment closest to the protein molecules is beneficial for an efficient bioprotective solution.

Stabilization of proteins embedded in sugars and water as studied by dielectric spectroscopy.

In many products proteins have become an important component, and the long-term properties of these products are directly dependent on the stability of their proteins. To enhance this stability it has become common to add disaccharides in general, and trehalose in particular. However, the mechanisms by which disaccharides stabilize proteins and other biological materials are still not fully understood, and therefore we have here used broadband dielectric spectroscopy to investigate the stabilizing effect of the disaccharides trehalose and sucrose on myoglobin, with the aim to enhance this understanding in general and to obtain specific insights into why trehalose exhibits extraordinary stabilizing properties. The results show the existence of three or four clearly observed relaxation processes, where the three common relaxations are the local (ß) water relaxation below the glass transition temperature (Tg), the structural α-relaxation of the solvent, observed above Tg, and an even slower protein relaxation due to large-scale conformational protein motions. For the trehalose containing samples with less than 50 wt% myoglobin a fourth relaxation process was observed due to a ß-relaxation of trehalose below Tg. This latter process, which was assigned to intramolecular rotations of the monosaccharide rings in trehalose, could not be detected for high protein concentrations or for the sucrose containing samples. Since sucrose has previously been found to form more intramolecular hydrogen bonds at the present hydration levels, it is likely that this rotation becomes too slow to be observed in the case of sucrose. However, this sugar relaxation has probably less influence on the protein stability below Tg, where the better stabilizing effect of trehalose on proteins can be explained by our observation that trehalose slows down the water relaxation more than sucrose does. Finally, we show that the α-relaxation of the solvent and the large-scale protein motions exhibit similar temperature dependences, which suggests that these protein motions are slaved by the α-relaxation. Furthermore, the α-relaxation of the trehalose solution is slower than for the corresponding sucrose solution, and thereby also the protein motions become slower in the trehalose solution, which explains the more efficient stabilizing effect of trehalose on proteins above Tg.

Motions of water and solutes-Slaving versus plasticization phenomena.

It is well-accepted that hydration water is crucial for the structure, dynamics, and function of proteins. However, the exact role of water for the motions and functions of proteins is still debated. Experiments have shown that protein and water dynamics are strongly coupled but with water motions occurring on a considerably faster time scale (the so-called slaving behavior). On the other hand, water also reduces the conformational entropy of proteins and thereby acts as a plasticizer of them. In this work, we analyze the dynamics (using broadband dielectric spectroscopy) of some specific non-biological water solutions in a broad concentration range to elucidate the role of water in the dynamics of the solutes. Our results demonstrate that at low water concentrations (less than 5 wt. %), the plasticization phenomenon prevails for all the materials analyzed. However, at higher water concentrations, two different scenarios can be observed: the slaving phenomenon or plasticization, depending on the solute analyzed. These results generalize the slaving phenomenon to some, but not all, non-biological solutions and allow us to analyze the key factors for observing the slaving behavior in protein solutions as well as to reshaping the slaving concept.

The White Matter Fiber Tract Deforms Most in the Perpendicular Direction During In Vivo Volunteer Impacts.

White matter (WM) tract-related strains are increasingly used to quantify brain mechanical responses, but their dynamics in live human brains during in vivo impact conditions remain largely unknown. Existing research primarily looked into the normal strain along the WM fiber tracts (i.e., tract-oriented normal strain), but it is rarely the case that the fiber tract only endures tract-oriented normal strain during impacts. In this study, we aim to extend the in vivo measurement of WM fiber deformation by quantifying the normal strain perpendicular to the fiber tract (i.e., tract-perpendicular normal strain) and the shear strain along and perpendicular to the fiber tract (i.e., tract-oriented shear strain and tract-perpendicular shear strain, respectively). To achieve this, we combine the three-dimensional strain tensor from the tagged magnetic resonance imaging with the diffusion tensor imaging (DTI) from an open-access dataset, including 44 volunteer impacts under two head loading modes, i.e., neck rotations (N = 30) and neck extensions (N = 14). The strain tensor is rotated to the coordinate system with one axis aligned with DTI-revealed fiber orientation, and then four tract-related strain measures are calculated. The results show that tract-perpendicular normal strain peaks are the largest among the four strain types (p < 0.05, Friedman's test). The distribution of tract-related strains is affected by the head loading mode, of which laterally symmetric patterns with respect to the midsagittal plane are noted under neck extensions, but not under neck rotations. Our study presents a comprehensive in vivo strain quantification toward a multifaceted understanding of WM dynamics. We find that the WM fiber tract deforms most in the perpendicular direction, illuminating new fundamentals of brain mechanics. The reported strain images can be used to evaluate the fidelity of computational head models, especially those intended to predict fiber deformation under noninjurious conditions.

Microscopic-scale magnetic recording of brain neuronal electrical activity using a diamond quantum sensor.

Quantum sensors using solid state qubits have demonstrated outstanding sensitivity, beyond that possible using classical devices. In particular, those based on colour centres in diamond have demonstrated high sensitivity to magnetic field through exploiting the field-dependent emission of fluorescence under coherent control using microwaves. Given the highly biocompatible nature of diamond, sensing from biological samples is a key interdisciplinary application. In particular, the microscopic-scale study of living systems can be possible through recording of temperature and biomagnetic field. In this work, we use such a quantum sensor to demonstrate such microscopic-scale recording of electrical activity from neurons in fragile living brain tissue. By recording weak magnetic field induced by ionic currents in mouse corpus callosum axons, we accurately recover signals from neuronal action potential propagation while demonstrating in situ pharmacology. Our sensor allows recording of the electrical activity in neural circuits, disruption of which can shed light on the mechanisms of disease emergence. Unlike existing techniques for recording activity, which can require potentially damaging direct interaction, our sensing is entirely passive and remote from the sample. Our results open a promising new avenue for the microscopic recording of neuronal signals, offering the eventual prospect of microscopic imaging of electrical activity in the living mammalian brain.

In-vitro Recordings of Neural Magnetic Activity From the Auditory Brainstem Using Color Centers in Diamond: A Simulation Study.

Magnetometry based on nitrogen-vacancy (NV) centers in diamond is a novel technique capable of measuring magnetic fields with high sensitivity and high spatial resolution. With the further advancements of these sensors, they may open up novel approaches for the 2D imaging of neural signals in vitro. In the present study, we investigate the feasibility of NV-based imaging by numerically simulating the magnetic signal from the auditory pathway of a rodent brainstem slice (ventral cochlear nucleus, VCN, to the medial trapezoid body, MNTB) as stimulated by both electric and optic stimulation. The resulting signal from these two stimulation methods are evaluated and compared. A realistic pathway model was created based on published data of the neural morphologies and channel dynamics of the globular bushy cells in the VCN and their axonal projections to the principal cells in the MNTB. The pathway dynamics in response to optic and electric stimulation and the emitted magnetic fields were estimated using the cable equation. For simulating the optic stimulation, the light distribution in brain tissue was numerically estimated and used to model the optogenetic neural excitation based on a four state channelrhodopsin-2 (ChR2) model. The corresponding heating was also estimated, using the bio-heat equation and was found to be low (<2°C) even at excessively strong optic signals. A peak magnetic field strength of ∼0.5 and ∼0.1 nT was calculated from the auditory brainstem pathway after electrical and optical stimulation, respectively. By increasing the stimulating light intensity four-fold (far exceeding commonly used intensities) the peak magnetic signal strength only increased to 0.2 nT. Thus, while optogenetic stimulation would be favorable to avoid artefacts in the recordings, electric stimulation achieves higher peak fields. The present simulation study predicts that high-resolution magnetic imaging of the action potentials traveling along the auditory brainstem pathway will only be possible for next generation NV sensors. However, the existing sensors already have sufficient sensitivity to support the magnetic sensing of cumulated neural signals sampled from larger parts of the pathway, which might be a promising intermediate step toward further maturing this novel technology.

Detection of biological signals from a live mammalian muscle using an early stage diamond quantum sensor.

The ability to perform noninvasive and non-contact measurements of electric signals produced by action potentials is essential in biomedicine. A key method to do this is to remotely sense signals by the magnetic field they induce. Existing methods for magnetic field sensing of mammalian tissue, used in techniques such as magnetoencephalography of the brain, require cryogenically cooled superconducting detectors. These have many disadvantages in terms of high cost, flexibility and limited portability as well as poor spatial and temporal resolution. In this work we demonstrate an alternative technique for detecting magnetic fields generated by the current from action potentials in living tissue using nitrogen vacancy centres in diamond. With 50 pT/[Formula: see text] sensitivity, we show the first measurements of magnetic sensing from mammalian tissue with a diamond sensor using mouse muscle optogenetically activated with blue light. We show these proof of principle measurements can be performed in an ordinary, unshielded lab environment and that the signal can be easily recovered by digital signal processing techniques. Although as yet uncompetitive with probe electrophysiology in terms of sensitivity, we demonstrate the feasibility of sensing action potentials via magnetic field in mammals using a diamond quantum sensor, as a step towards microscopic imaging of electrical activity in a biological sample using nitrogen vacancy centres in diamond.

Structural Comparison between Sucrose and Trehalose in Aqueous Solution.

The two sugar molecules sucrose and trehalose are both considered as stabilizing molecules for the purpose of preserving biological materials during, for example, lyophilization or cryo-preservation. Although these molecules share a similar molecular structure, there are several important differences in their properties when they interact with water, such as differences in solubility, viscosity, and glass transition temperature. In general, trehalose has been shown to be more efficient than other sugar molecules in preserving different biological molecules against stress, and thus by investigating how these two disaccharides differ in their water interaction, it is possible to further understand what makes trehalose special in its stabilizing properties. For this purpose, the structure of aqueous solutions of these disaccharides was studied by using neutron and X-ray diffraction in combination with empirical potential structure refinement (EPSR) modeling. The results show that there are surprisingly few differences in the overall structure of the solutions, although there are indications for that trehalose perturbs the water structure slightly more than sucrose.

Mechanism of Trehalose-Induced Protein Stabilization from Neutron Scattering and Modeling.

The sugar molecule trehalose has been proven to be an excellent stabilizing cosolute for the preservation of biological materials. However, the stabilizing mechanism of trehalose has been much debated during the previous decades, and it is still not fully understood, partly because it has not been completely established how trehalose molecules structure around proteins. Here, we present a molecular model of a protein-water-trehalose system, based on neutron scattering results obtained from neutron diffraction, quasielastic neutron scattering, and different computer modeling techniques. The structural data clearly show how the proteins are preferentially hydrated, and analysis of the dynamical properties show that the protein residues are slowed down because of reduced dynamics of the protein hydration shell, rather than because of direct trehalose-protein interactions. These findings, thereby, strongly support previous models related to the preferential hydration model and contradict other models based on water replacement at the protein surface. Furthermore, the results are important for understanding the specific role of trehalose in biological stabilization and, more generally, for providing a likely mechanism of how cosolutes affect the dynamics of proteins.

The Role of Trehalose for the Stabilization of Proteins.

Understanding of how the stabilization mechanism of trehalose operates on biological molecules against different types of environmental stress could prove to gain great advancements in many different types of conservation techniques, such as cryopreservation or freeze-drying. Many theories exist that aim to explain why trehalose possesses an extraordinary ability to stabilize biomolecules. However, all of them just explain parts of its mechanism and a comprehensive picture is still lacking. In this study, we have used differential scanning calorimetry (DSC) and viscometry measurements to determine how the glass transition temperature Tg, the protein denaturation temperature Tden, and the dynamic viscosity depend on both the trehalose and the protein concentration in myoglobin-trehalose-water systems. The aim has been to determine whether these physical properties are related and to gain indirect structural insights from the limits of water crystallization at different concentration ratios. The results show that for systems without partial crystallization of water the addition of protein increases Tg, most likely due to the fact that the protein adsorbs water and thereby reduces the water content in the trehalose-water matrix. Furthermore, these systems are generally decreasing in Tden with an increasing protein concentration, and thereby also an increasing viscosity, showing that the dynamics of the trehalose-water matrix and the stability of the native structure of the protein are not necessarily coupled. We also infer, by analyzing the maximum amount of water for which ice formation is avoided, that the preferential hydration model is consistent with our experimental data.

Structure of Aqueous Trehalose Solution by Neutron Diffraction and Structural Modeling.

The molecular structure of an aqueous solution of the disaccharide trehalose (C12H22O11) has been studied by neutron diffraction and empirical potential structure refinement modeling. Six different isotope compositions with 33 wt % trehalose (corresponding to 38 water molecules per trehalose molecule) were measured to ensure that water-water, trehalose-water, and trehalose-trehalose correlations were accurately determined. In fact, this is the first neutron diffraction study of an aqueous trehalose solution in which also the nonexchangeable hydrogen atoms in trehalose are deuterated. With this approach, it was possible to determine that (1) there is a substantial hydrogen bonding between trehalose and water (∼11 hydrogen bonds per trehalose molecule), which is in contrast to previous neutron diffraction studies, and (2) there is no tendency of clustering of trehalose, in contrast to what is generally observed by molecular dynamics simulations and experimentally found for other disaccharides. Thus, the results give the structural picture that trehalose prefers to interact with water and participate in a hydrogen-bonded network. This strong network character of the solution might be one of the key reasons for its extraordinary stabilization effect on biological materials.