Thermal denaturation of myoglobin in water--disaccharide matrixes: relation with the glass transition of the system

Near UV and Visible Light Photodegradation in Solid Formulations: Generation of Carbon Dioxide Radical Anions from Citrate Buffer and Fe(III)

Near UV and visible light photodegradation can target therapeutic proteins during manufacturing and storage. While the underlying photodegradation pathways are frequently not well-understood, one important aspect of consideration is the formulation, specifically the formulation buffer. Citrate is a common buffer for biopharmaceutical formulations, which can complex with transition metals, such as Fe(III). In an aqueous solution, the exposure of such complexes to light leads to the formation of the carbon dioxide radical anion (•CO2-), a powerful reductant. However, few studies have characterized such processes in solid formulations. Here, we show that solid citrate formulations containing Fe(III) lead to the photochemical formation of •CO2-, identified through DMPO spin trapping and HPLC-MS/MS analysis. Factors such as buffers, the availability of oxygen, excipients, and manufacturing processes of solid formulations were evaluated for their effect on the formation of •CO2- and other radicals such as •OH.

Comparison of Sucrose and Trehalose for Protein Stabilization Using Differential Scanning Calorimetry

The disaccharide trehalose is generally acknowledged as a superior stabilizer of proteins and other biomolecules in aqueous environments. Despite many theories aiming to explain this, the stabilization mechanism is still far from being fully understood. This study compares the stabilizing properties of trehalose with those of the structurally similar disaccharide sucrose. The stability has been evaluated for the two proteins, lysozyme and myoglobin, at both low and high temperatures by determining the glass transition temperature, Tg, and the denaturation temperature, Tden. The results show that the sucrose-containing samples exhibit higher Tden than the corresponding trehalose-containing samples, particularly at low water contents. The better stabilizing effect of sucrose at high temperatures may be explained by the fact that sucrose, to a greater extent, binds directly to the protein surface compared to trehalose. Both sugars show Tden elevation with an increasing sugar-to-protein ratio, which allows for a more complete sugar shell around the protein molecules. Finally, no synergistic effects were found by combining trehalose and sucrose. Conclusively, the exact mechanism of protein stabilization may vary with the temperature, as influenced by temperature-dependent interactions between the protein, sugar, and water. This variability can make trehalose to a superior stabilizer under some conditions and sucrose under others.

Protecting Proteins from Desiccation Stress Using Molecular Glasses and Gels

Faced with desiccation stress, many organisms deploy strategies to maintain the integrity of their cellular components. Amorphous glassy media composed of small molecular solutes or protein gels present general strategies for protecting against drying. We review these strategies and the proposed molecular mechanisms to explain protein protection in a vitreous matrix under conditions of low hydration. We also describe efforts to exploit similar strategies in technological applications for protecting proteins in dry or highly desiccated states. Finally, we outline open questions and possibilities for future explorations.

A Long Journey into the Investigation of the Structure–Dynamics–Function Paradigm in Proteins through the Activities of the Palermo Biophysics Group

An overview of the biophysics activity at the Department of Physics and Chemistry Emilio Segrè of the University of Palermo is given. For forty years, the focus of the research has been on the protein structure–dynamics–function paradigm, with the aim of understanding the molecular basis of the relevant mechanisms and the key role of solvent. At least three research lines are identified; the main results obtained in collaboration with other groups in Italy and abroad are presented. This review is dedicated to the memory of Professors Massimo Ugo Palma, Maria Beatrice Palma Vittorelli, and Lorenzo Cordone, which were the founders of the Palermo School of Biophysics. We all have been, directly or indirectly, their pupils; we miss their enthusiasm for scientific research, their deep physical insights, their suggestions, their strict but always constructive criticisms, and, most of all, their friendship. This paper is dedicated also to the memory of Prof. Hans Frauenfelder, whose pioneering works on nonexponential rebinding kinetics, protein substates, and energy landscape have inspired a large part of our work in the field of protein dynamics.

"Water Association" Band in Saccharide Amorphous Matrices: Role of Residual Water on Bioprotection

Saccharides protect biostructures against adverse environmental conditions mainly by preventing large scale motions leading to unfolding. The efficiency of this molecular mechanism, which is higher in trehalose with respect to other sugars, strongly depends on hydration and sugar/protein ratio. Here we report an Infrared Spectroscopy study on dry amorphous matrices of the disaccharides trehalose, maltose, sucrose and lactose, and the trisaccharide raffinose. Samples with and without embedded protein (Myoglobin) are investigated at different sugar/protein ratios, and compared. To inspect matrix properties we analyse the Water Association Band (WAB), and carefully decompose it into sub-bands, since their relative population has been shown to effectively probe water structure and dynamics in different matrices. In this work the analysis is extended to investigate the structure of protein-sugar-water samples, for the first time. Results show that several classes of water molecules can be identified in the protein and sugar environment and that their relative population is dependent on the type of sugar and, most important, on the sugar/protein ratio. This gives relevant information on how the molecular interplay between residual waters, sugar and protein molecules affect the biopreserving properties of saccharides matrices.

Lyophilization stabilizes clinical-stage core-crosslinked polymeric micelles to overcome cold chain supply challenges

BACKGROUND

CriPec technology enables the generation of drug-entrapped biodegradable core-crosslinked polymeric micelles (CCPM) with high drug loading capacity, tailorable size, and drug release kinetics. Docetaxel (DTX)-entrapped CCPM, also referred to as CPC634, have demonstrated favorable pharmacokinetics, tolerability, and enhanced tumor uptake in patients. Clinical efficacy evaluation is ongoing. CPC634 is currently stored (shelf life > 5 years) and shipped as a frozen aqueous dispersion at temperatures below -60°C, in order to prevent premature release of DTX and hydrolysis of the core-crosslinks. Consequently, like other aqueous nanomedicine formulations, CPC634 relies on cold chain supply, which is unfavorable for commercialization. Lyophilization can help to bypass this issue.

METHODS AND RESULTS

Freeze-drying methodology for CCPM was developed by employing CPC634 as a model formulation, and sucrose and trehalose as cryoprotectants. We studied the residual moisture content and reconstitution behavior of the CPC634 freeze-dried cake, as well as the size, polydispersity index, morphology, drug retention, and release kinetics of reconstituted CPC634. Subsequently, the freeze-drying methodology was validated in an industrial setting, yielding a CPC634 freeze-dried cake with a moisture content of less than 0.1 wt%. It was found that trehalose-cryoprotected CPC634 could be rapidly reconstituted in less than 5 min at room temperature. Critical quality attributes such as size, morphology, drug retention, and release kinetics of trehalose-cryoprotected freeze-dried CPC634 upon reconstitution were identical to those of non-freeze-dried CPC634.

CONCLUSION

Our findings provide proof-of-concept for the lyophilization of drug-containing CCPM and our methodology is readily translatable to large-scale manufacturing for future commercialization.

Technologies and Applications Toward Preservation of Cells in a Dry State for Therapies

Cell-based therapeutics promise to transform the treatment of a wide range of diseases, many of which, up to this point, are incurable. During the past decade, an increasing number of cell therapies have been approved by government regulatory agencies in the United States, Europe, and Japan. Thousands of clinical trials based on live cell therapies are now taking place around the world. But most of these live cell therapies face temporal and/or spatial distances between manufacture and administration, posing a risk of degradation in potency. Cryopreservation has become the predominant biobanking approach to maintain the product's safety and efficacy during transportation and storage. However, the necessity of cryogenic shipment and storage could limit patient access to these emerging therapies and increase the costs of logistics. In the (bio)pharmaceutical industries, freeze-drying and desiccation are established preservation procedures for manufacturing small molecule drugs, liposomes, and monoclonal antibodies. Over the past two decades, there has been a growing body of research exploring the freeze-drying or drying of mammalian cells, with varying degrees of success. This article provides an overview of the technologies that were adopted or developed in these pioneering studies, paving the road toward the preservation of cell-based therapeutics in a dry state for biomanufacturing.

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 (β) 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 β-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.

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.

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

Catalysis makes chemical and biochemical reactions kinetically accessible. From a technological point of view, organic, inorganic, and biochemical catalysis is relevant for several applications, from industrial synthesis to biomedical, material, and food sciences. A heterogeneous catalyst, i.e., a catalyst confined in a different phase with respect to the reagents’ phase, requires either its physical confinement in an immobilization matrix or its physical adsorption on a surface. In this review, we will focus on the immobilization of biological catalysts, i.e., enzymes, by comparing hard and soft immobilization matrices and their effect on the modulation of the catalysts’ function. Indeed, unlike smaller molecules, the catalytic activity of protein catalysts depends on their structure, conformation, local environment, and dynamics, properties that can be strongly affected by the immobilization matrices, which, therefore, not only provide physical confinement, but also modulate catalysis.

Bioprotection Can Be Tuned with a Proper Protein/Saccharide Ratio: The Case of Solid Amorphous Matrices

Saccharides, and in particular trehalose, are well known for their high efficiency in protecting biostructures against adverse environmental conditions. The protein dynamics is known to be highly inhibited in a low-water trehalose host medium, the inhibition being markedly dependent on the amount of residual water. Besides hydration, the protein/sugar ratio is expected to affect the properties of saccharide amorphous matrices. In this work, we report an infrared spectroscopy study in dry amorphous matrices of various sugars (the disaccharides trehalose, maltose, sucrose, and lactose, and the trisaccharide raffinose) containing myoglobin, at different protein/sugar ratios. We analyze the stretching band of the bound CO molecule and the water association band. Such bands have already been successfully exploited for the simultaneous study of thermal evolution of a matrix and embedded protein. The results show a high dependence of protein and matrix signals on the protein/sugar ratio, the system behavior evolving from situations where (i) the protein slaves the matrix to (ii) protein ↔ matrix coupling/uncoupling, then to (iii) the matrix slaving the protein, with increasing sugar concentration. This supports a mutual protein ↔ matrix structural and dynamic influence in low hydrated systems, indicating that the protein/solvent master and slave paradigm does not strictly hold, but the mutual relationship depends on the relative concentrations. Furthermore, for each sugar, an optimal protein/sugar concentration ratio can be identified, which maximizes the protein preservation; under such a condition, the water content is minimal.

Biopreservation of Myoglobin in Crowded Environment: A Comparison between Gelatin and Trehalose Matrixes

Biopreservation by sugar and/or polymeric matrixes is a thoroughly studied research topic with wide technological relevance. Ternary amorphous systems containing both saccharides and proteins are extensively exploited to model the in vivo biopreservation process. With the aim of disentangling the effect of saccharides and polypeptidic crowders (such as gelatin) on the preservation of a model protein, we present here a combined differential scanning calorimetry and UV-vis spectrophotometry study on samples of myoglobin embedded in amorphous gelatin and trehalose + gelatin matrixes at different hydrations, and compare them with amorphous myoglobin-only and myoglobin-trehalose samples. The results point out the different effects of gelatin, which acts mainly as a crowding agent, and trehalose, which acts mainly by direct interaction. Gelatin is able to improve effectively the protein thermal stability at very low hydration; however, it has small effects at medium to high hydration. Consistently, gelatin appears to be more effective than trehalose against massive denaturation in the long time range, while the mixed trehalose + collagen matrix is most effective in preserving protein functionality, outdoing both gelatin-only and trehalose-only matrixes.

The amorphous state: first-principles derivation of the Gordon–Taylor equation for direct prediction of the glass transition temperature of mixtures; estimation of the crossover temperature of fragile glass formers; physical basis of the “Rule of 2/3”

Predicting the glass transition and crossover temperatures of pure amorphous phases and mixtures finds broad application across different fields of study.

The water association band as a marker of hydrogen bonds in trehalose amorphous matrices

The water association band is a suitable marker of residual water behavior in bioprotective trehalose matrices.

Dynamic and thermodynamic characteristics associated with the glass transition of amorphous trehalose-water mixtures

The glass transition temperature Tg of biopreservative formulations is important for predicting the long-term storage of biological specimens. As a complementary tool to thermal analysis techniques, which are the mainstay for determining Tg, molecular dynamics simulations have been successfully applied to predict the Tg of several protectants and their mixtures with water. These molecular analyses, however, rarely focused on the glass transition behavior of aqueous trehalose solutions, a subject that has attracted wide scientific attention via experimental approaches. Important behavior, such as hydrogen-bonding dynamics and self-aggregation has yet to be explored in detail, particularly below, or in the vicinity of, Tg. Using molecular dynamics simulations of several dynamic and thermodynamic properties, this study reproduced the supplemented phase diagram of trehalose-water mixtures (i.e., Tg as a function of the solution composition) based on experimental data. The structure and dynamics of the hydrogen-bonding network in the trehalose-water systems were also analyzed. The hydrogen-bonding lifetime was determined to be an order of magnitude higher in the glassy state than in the liquid state, while the constitution of the hydrogen-bonding network exhibited no noticeable change through the glass transition. It was also found that trehalose molecules preferred to form small, scattered clusters above Tg, but self-aggregation was substantially increased below Tg. The average cluster size in the glassy state was observed to be dependent on the trehalose concentration. Our findings provided insights into the glass transition characteristics of aqueous trehalose solutions as they relate to biopreservation.

Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry

We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide L-alanyl-L-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide.

Theoretical–computational modelling of the electric field effects on protein unfolding thermodynamics

In this paper we present a general theoretical–computational approach to model the protein unfolding thermodynamics response to intense electric fields.

Structural and dynamical characteristics of trehalose and sucrose matrices at different hydration levels as probed by FTIR and high-field EPR

Some organisms can survive complete dehydration and high temperatures by adopting an anhydrobiotic state in which the intracellular medium contains large amounts of disaccharides, particularly trehalose and sucrose. Trehalose is most effective also in protecting isolated in vitro biostructures. In an attempt to clarify the molecular mechanisms of disaccharide bioprotection, we compared the structure and dynamics of sucrose and trehalose matrices at different hydration levels by means of high-field W-band EPR and FTIR spectroscopy. The hydration state of the samples was characterized by FTIR spectroscopy and the structural organization was probed by EPR using a nitroxide radical dissolved in the respective matrices. Analysis of the EPR spectra showed that the structure and dynamics of the dehydrated matrices as well as their evolution upon re-hydration differ substantially between trehalose and sucrose. The dehydrated trehalose matrix is homogeneous in terms of distribution of the residual water and spin-probe molecules. In contrast, dehydrated sucrose forms a heterogeneous matrix. It is comprised of sucrose polycrystalline clusters and several bulk water domains. The amorphous form was found only in 30% (volume) of the sucrose matrix. Re-hydration leads to a structural homogenization of the sucrose matrix, whilst in the trehalose matrix several domains develop differing in the local water/radical content and radical mobility. The molecular model of the matrices provides an explanation for the different protein-matrix dynamical coupling observed in dried ternary sucrose and trehalose matrices, and accounts for the superior efficacy of trehalose as a bioprotectant. Furthermore, for bacterial photosynthetic reaction centers it is shown that at low water content the protein-matrix coupling is modulated by the sugar/protein molar ratio in sucrose matrices only. This effect is suggested to be related to the preference for sucrose, rather than trehalose, as a bioprotective disaccharide in some anhydrobiotic organisms.

Hydration dependence of myoglobin dynamics studied with elastic neutron scattering, differential scanning calorimetry and broadband dielectric spectroscopy

In this work we present a thorough investigation of the hydration dependence of myoglobin dynamics. The study is performed on D2O-hydrated protein powders in the hydration range 0<h<0.5 (h≡gr[D2O]/gr[protein]) and in the temperature range 20-300K. The protein equilibrium fluctuations are investigated with Elastic Neutron Scattering using the spectrometer IN13 at ILL (Grenoble), while the relaxations of the protein+hydration water system are investigated with Broadband Dielectric Spectroscopy; finally, Differential Scanning Calorimetry is used to obtain a thermodynamic description of the system. The effect of increasing hydration is to speed up the relaxations of the myoglobin+hydration water system and, thermodynamically, to decrease the glass transition temperature; these effects tend to saturate at h values greater than ~0.3. Moreover, the calorimetric scans put in evidence the occurrence of an endothermic peak whose onset temperature is located at ~230K independent of hydration. From the point of view of the protein equilibrium fluctuations, while the amplitude of anharmonic mean square displacements is found to increase with hydration, their onset temperature (i.e. the onset temperature of the well known "protein dynamical transition") is hydration independent. On the basis of the above results, the relevance of protein+hydration water relaxations and of the thermodynamic state of hydration water to the onset of the protein dynamical transition is discussed.

Proteins in amorphous saccharide matrices: structural and dynamical insights on bioprotection

Bioprotection by sugars, and in particular trehalose peculiarity, is a relevant topic due to the implications in several fields. The underlying mechanisms are not yet clearly elucidated, and remain the focus of current investigations. Here we revisit data obtained at our lab on binary sugar/water and ternary protein/sugar/water systems, in wide ranges of water content and temperature, in the light of the current literature. The data here discussed come from complementary techniques (Infrared Spectroscopy, Molecular Dynamics simulations, Small Angle X-ray Scattering and Calorimetry), which provided a consistent description of the bioprotection by sugars from the atomistic to the macroscopic level. We present a picture, which suggests that protein bioprotection can be explained in terms of a strong coupling of the biomolecule surface to the matrix via extended hydrogen-bond networks, whose properties are defined by all components of the systems, and are strongly dependent on water content. Furthermore, the data show how carbohydrates having similar hydrogen-bonding capabilities exhibit different efficiency in preserving biostructures.

How strongly does trehalose interact with lysozyme in the solid state? Insights from molecular dynamics simulation and inelastic neutron scattering

Therapeutic proteins are usually conserved in glassy matrixes composed of stabilizing excipients and a small amount of water, which both control their long-term stability, and thus their potential use in medical treatments. To shed some light on the protein-matrix interactions in such systems, we performed molecular dynamics (MD) simulations on matrixes of (i) the model globular protein lysozyme (L), (ii) the well-known bioprotectant trehalose (T), and (iii) the 1:1 (in weight) lysozyme/trehalose mixture (LT), at hydration levels h of 0.0, 0.075, and 0.15 (in g of water/g of protein or sugar). We also supplemented these simulations with complementary inelastic neutron scattering (INS) experiments on the L, T, and LT lyophilized (freeze-dried) samples. The densities and free volume distributions indicate that trehalose improves the molecular packing of the LT glass with respect to the L one. Accordingly, the low-frequency vibrational densities of states (VDOS) and the mean square displacements (MSDs) of lysozyme reveal that it is less flexible-and thus less likely to unfold-in the presence of trehalose. Furthermore, at low contents (h = 0.075), water systematically stiffens the vibrational motions of lysozyme and trehalose, whereas it increases their MSDs on the nanosecond (ns) time scale. This stems from the hydrogen bonds (HBs) that lysozyme and trehalose form with water, which, interestingly, are stronger than the ones they form with each other but which, nonetheless, relax faster on the ns time scale, given the larger mobility of water. Moreover, lysozyme interacts preferentially with water in the hydrated LT mixtures, and trehalose appears to slow down significantly the relaxation of lysozyme-water HBs. Overall, our results suggest that the stabilizing efficiency of trehalose arises from its ability to (i) increase the number of HBs formed by proteins in the dry state and (ii) make the HBs formed by water with proteins stable on long (>ns) time scales.

Interfacial viscoelasticity of myoglobin at air/water and air/solution interfaces: role of folding and clustering

This study describes the folding and organization of myoglobin (Mb) at the solution/air interface at different pH values of 2.5, 3.5, 5.5, 7.5, and 8.5. Dynamic surface tension and the associated dilational and shear viscoelasticity for Mb at these pH's have been studied using a sinusoidal surface compression and expansion for frequencies ranging from 0.01 to 0.4 Hz. The changes in dilational viscosity, elasticity, and fluorescence lifetime measurements have been related to the conformational changes of the protein films at the interface. It is observed that while acid-induced denaturation of the protein does not lead to large changes in dilational properties, the shear properties on the other hand are strongly influenced by it, and the protein behaves like a shear-thickening fluid. At higher pH, particularly at the isoelectric point, Mb is pseudoplastic indicating an increase in the shear viscosity. These results are strongly suggestive of formation of hydrophobic clusters at the protein-buffer interface because of the change in the overall charge distributions.

SAXS study on myoglobin embedded in amorphous saccharide matrices

We report on Small Angle X-ray Scattering (SAXS) measurements performed on samples of carboxy-myoglobin and met-myoglobin embedded in low hydrated matrices of four different saccharides (trehalose, sucrose, maltose and lactose). Results confirm the already reported occurrence of inhomogeneities, which are not peculiar of trehalose samples, but appear also in maltose and lactose, and in some cases also sucrose, being dependent on the sample hydration and on the presence of sodium dithionite. This behaviour confirms our previous interpretation about the nature of the inhomogeneities, and prompt it as a possible general behaviour for highly concentrated sugar matrices.

Protein thermal denaturation and matrix glass transition in different protein-trehalose-water systems

Biopreservation by saccharides is a widely studied issue due to its scientific and technological importance; in particular, ternary amorphous protein-saccharide-water systems are extensively exploited to model the characteristics of the in vivo biopreservation process. We present here a differential scanning calorimetry (DSC) study on amorphous trehalose-water systems with embedded different proteins (myoglobin, lysozyme, BSA, hemoglobin), which differ for charge, surface, and volume properties. In our study, the protein/trehalose molar ratio is kept constant at 1/40, while the water/sugar molar ratio is varied between 2 and 300; results are compared with those obtained for binary trehalose-water systems. DSC upscans offer the possibility of investigating, in the same measurement, the thermodynamic properties of the matrix (glass transition, T(g)) and the functional properties of the encapsulated protein (thermal denaturation, T(den)). At high-to-intermediate hydration, the presence of the proteins increases the glass transition temperature of the encapsulating matrix. The effect mainly depends on size properties, and it can be ascribed to confinement exerted by the protein on the trehalose-water solvent. Conversely, at low hydration, lower T(g) values are measured in the presence of proteins: the lack of water promotes sugar-protein interactions, thus weakening the confinement effect and softening the matrix with respect to the binary system. A parallel T(den) increase is also observed; remarkably, this stabilization can reach ∼70 K at low hydration, a finding potentially of high biotechnological relevance. A linear relationship between T(g) and T(den) is also observed, in line with previous results; this finding suggests that collective water-trehalose interactions, responsible for the glass transition, also influence the protein denaturation.

Myoglobin embedded in saccharide amorphous matrices: water-dependent domains evidenced by small angle X-ray scattering

We report Small Angle X-ray Scattering (SAXS) measurements performed on samples of carboxy-myoglobin (MbCO) embedded in low-water trehalose glasses. Results showed that, in such samples, "low-protein" trehalose-water domains are present, surrounded by a protein-trehalose-water background; such finding is supported by Infrared Spectroscopy (FTIR) measurements. These domains, which do not appear in the absence of the protein and in analogous sucrose systems, preferentially incorporate the incoming water at the onset of rehydration, and disappear following large hydration. This observation suggests that, in organisms under anhydrobiosis, analogous domains could play a buffering role against the daily variations of the atmospheric moisture. The reported results are rationalized by assuming sizably different protein-matrix coupling in trehalose with respect to sucrose, analogous to the one suggested for the photosynthetic reaction centre from Rhodobacter sphaeroides (F. Francia et al., J. Am. Chem. Soc., 2008, 130, 10240-10246).