Protection against Dehydration: A Neutron Diffraction Study on Aqueous Solutions of a Model Peptide and Trehalose

Evidence of Correlation between Membrane Phase Transition and Clonogenicity in Dehydrating Acinetobacter baumannii: A Combined Micro-Raman and AFM Study

The Gram-negative bacterium Acinetobacter baumannii is one of the most resilient multidrug-resistant pathogens in hospitals. Among Gram-negative bacteria, it is particularly resistant to dehydration (anhydrobiosis), and this feature allows A. baumannii to persist in hospital environments for long periods, subjected to unfavorable conditions. We leverage the combination of μ-Raman spectroscopy and atomic force microscopy (AFM) to investigate the anhydrobiotic mechanisms in A. baumannii cells by monitoring the membrane (both inner and outer membranes) properties of four A. baumannii strains during a 16-week dehydration period and in response to temperature excursions. We noted that the membranes of A. baumannii remained intact during the dehydration period despite undergoing a liquid-crystal-to-gel-phase transition, accompanied by changes in the mechanical properties of the membrane. This was evident from the AFM images, which showed the morphology of the bacterial cells alongside modifications of their superficial mechanical properties, and from the alteration in the intensity ratio of μ-Raman features linked to the CH3 and CH2 symmetric stretching modes. Furthermore, employing a universal power law revealed a significant correlation between this ratio and bacterial fitness across all tested strains. Additionally, we subjected dry A. baumannii to a temperature-dependent experiment, the results of which supported the correlation between the Raman ratio and culturability, demonstrating that the phase transition becomes irreversible when A. baumannii cells undergo different temperature cycles. Besides the relevance to the present study, we argue that μ-Raman can be used as a powerful nondestructive tool to assess the health status of bacterial cells based on membrane properties with a relatively high throughput.

Trimethylamine-N-oxide depletes urea in a peptide solvation shell

Trimethylamine-N-oxide (TMAO) and urea are metabolites that are used by some marine animals to maintain their cell volume in a saline environment. Urea is a well-known denaturant, and TMAO is a protective osmolyte that counteracts urea-induced protein denaturation. TMAO also has a general protein-protective effect, for example, it counters pressure-induced protein denaturation in deep-sea fish. These opposing effects on protein stability have been linked to the spatial relationship of TMAO, urea, and protein molecules. It is generally accepted that urea-induced denaturation proceeds through the accumulation of urea at the protein surface and their subsequent interaction. In contrast, it has been suggested that TMAO's protein-stabilizing effects stem from its exclusion from the protein surface, and its ability to deplete urea from protein surfaces; however, these spatial relationships are uncertain. We used neutron diffraction, coupled with structural refinement modeling, to study the spatial associations of TMAO and urea with the tripeptide derivative glycine-proline-glycinamide in aqueous urea, aqueous TMAO, and aqueous urea-TMAO (in the mole ratio 1:2 TMAO:urea). We found that TMAO depleted urea from the peptide's surface and that while TMAO was not excluded from the tripeptide's surface, strong atomic interactions between the peptide and TMAO were limited to hydrogen bond donating peptide groups. We found that the repartition of urea, by TMAO, was associated with preferential TMAO-urea bonding and enhanced urea-water hydrogen bonding, thereby anchoring urea in the bulk solution and depleting urea from the peptide surface.

How Sugars Protect Dry Protein Structure

Extremotolerant organisms and industry exploit sugars as desiccation protectants, with trehalose being widely used by both. How sugars, in general, and the hydrolytically stable sugar trehalose, in particular, protect proteins is poorly understood, which hinders the rational design of new excipients and implementation of novel formulations for preserving lifesaving protein drugs and industrial enzymes. We employed liquid-observed vapor exchange nuclear magnetic resonance (LOVE NMR), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) to show how trehalose and other sugars protect two model proteins: the B1 domain of streptococcal protein G (GB1) and truncated barley chymotrypsin inhibitor 2 (CI2). Residues with intramolecular H-bonds are most protected. The LOVE NMR and DSC data indicate that vitrification may be protective. Combining LOVE NMR and TGA data shows that water retention is not important. Our data suggest that sugars protect protein structure as they dry by strengthening intraprotein H-bonds and water replacement and that trehalose is the stress-tolerance sugar of choice because of its covalent stability.

Spectroscopic evidence of the radioresistance of Chroococcidiopsis biosignatures: A combined Raman, FT-IR and THz-TDs spectroscopy study

In the last decades, Mars has been widely studied with on-site missions and observations, showing a planet that could have hosted life in the past. For this reason, the recent and future space missions on the red planet will search for traces of past and, possibly, present life. As a basis for these missions, Space Agencies, such as the European Space Agency, have conducted many experiments on living organisms, studying their behavior in extraterrestrial conditions, learning to recognize their biosignatures with techniques remotely controllable such as Raman spectroscopy. Among these organisms, the radioresistant cyanobacterium Chroococcidiopsis was irradiated during the STARLIFE campaign with strong radiative insults. In this article we have investigated this cyanobacterium using Raman spectroscopy and extended the characterization of its biosignatures and its response to the radiative stress to the mid- Infrared and Terahertz spectral region using the Fourier Transform InfraRed (FT-IR) and Terahertz Time Domain spectroscopy (THz- TDs), which demonstrates the compatibility and suitability of these techniques for future space missions.

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.

Development of Icephilic ACTIVE Glycopeptides for Cryopreservation of Human Erythrocytes

Ice formation and recrystallization exert severe impairments to cellular cryopreservation. In light of cell-damaging washing procedures in the current glycerol approach, many researches have been devoted to the development of biocompatible cryoprotectants for optimal bioprotection of human erythrocytes. Herein, we develop a novel ACTIVE glycopeptide of saccharide-grafted ε-poly(L-lysine), that can be credited with adsorption on membrane surfaces, cryopreservation with trehalose, and icephilicity for validity of human erythrocytes. Then, by Borch reductive amination or amidation, glucose, lactose, maltose, maltotriose, or trehalose was tethered to ε-polylysine. The synthesized ACTIVE glycopeptides with intrinsic icephilicity could localize on the membrane surface of human erythrocytes and improve cryopreservation with trehalose, so that remarkable post-thaw cryosurvival of human erythrocytes was achieved with a slight variation in cell morphology and functions. Human erythrocytes (∼50% hematocrit) in cryostores could maintain high cryosurvival above 74%, even after plunged in liquid nitrogen for 6 months. Analyses of differential scanning calorimetry, Raman spectroscopy, and dynamic ice shaping suggested that this cryopreservation protocol combined with the ACTIVE glycopeptide and trehalose could enhance the hydrogen bond network in nonfrozen solutions, resulting in inhibition of recrystallization and growth of ice. Therefore, the ACTIVE glycopeptide can be applied as a trehalose-associated "chaperone", providing a new way to serve as a candidate in glycerol-free human erythrocyte cryopreservation.

Protein Hydration in a Bioprotecting Mixture

We combined broad-band depolarized light scattering and infrared spectroscopies to study the properties of hydration water in a lysozyme-trehalose aqueous solution, where trehalose is present above the concentration threshold (30% in weight) relevant for biopreservation. The joint use of the two different techniques, which were sensitive to inter-and intra-molecular degrees of freedom, shed new light on the molecular mechanism underlying the interaction between the three species in the mixture. Thanks to the comparison with the binary solution cases, we were able to show that, under the investigated conditions, the protein, through preferential hydration, remains strongly hydrated even in the ternary mixture. This supported the water entrapment scenario, for which a certain amount of water between protein and sugar protects the biomolecule from damage caused by external agents.

Poly 2-methacryloyloxyethyl Phosphorylcholine Protects Corneal Cells and Contact Lenses from Desiccation Damage

SIGNIFICANCE

Contact lens (CL) wearing may cause discomfort and eye dryness. We describe here the efficacy of a synthetic polymer in protecting both the corneal epithelial cells and the CL from desiccation damage. Artificial tears containing this polymer might be helpful to treat or prevent ocular surface damage in CL wearers.

PURPOSE

We aimed to investigate the protective effects of the synthetic polymer 2-methacryloyloxyethyl phosphorylcholine (poly-MPC) on corneal epithelial cells and CLs subjected to desiccation damage.

METHODS

The interaction of poly-MPC with the cell membrane was evaluated on human primary corneal epithelial cells (HCE-F) by the sodium dodecyl sulfate damage protection assay or the displacement of the cell-binding lectin concanavalin A (ConA). Survival in vitro of HCE-F cells and ex vivo of porcine corneas exposed to desiccating conditions after pre-treatment with poly-MPC or hyaluronic acid (HA), hypromellose (HPMC), and trehalose was evaluated by a colorimetric assay. Soft CLs were soaked overnight in a solution of poly-MPC/HPMC and then let dry in ambient air. Contact lens weight, morphology, and transparency were periodically registered until complete dryness.

RESULTS

Polymer 2-methacryloyloxyethyl phosphorylcholine and HPMC were retained on the HCE-F cell membrane more than trehalose or HA. Polymer 2-methacryloyloxyethyl phosphorylcholine, HA, and HPMC either alone or in association protected corneal cells from desiccation significantly better than did trehalose alone or in association with HA. Contact lens permeation by poly-MPC/HPMC preserved better their shape and transparency than did saline.

CONCLUSIONS

Polymer 2-methacryloyloxyethyl phosphorylcholine coats and protects corneal epithelial cells and CLs from desiccation damage more efficiently compared with trehalose and as good as other reference compounds.

Prebiotic Lactulose Ameliorates the Cognitive Deficit in Alzheimer's Disease Mouse Model through Macroautophagy and Chaperone-Mediated Autophagy Pathways

Lactulose, as a prebiotic, can be utilized by human gut microbiota and stimulate their growth. Although microbiota modulation has become an emerging approach to manage many diseases and can be achieved by the administration of prebiotics, fewer investigations have been carried out on the therapeutic mechanism of lactulose. Two trehalose analogs, lactulose and melibiose, were identified as having a neuroprotective effect in polyglutamine and Parkinson disease models. In this study, we examined lactulose and melibiose in a mouse primary hippocampal neuronal culture under the toxicity of oligomeric Aβ_25-35. Lactulose was further tested in vivo because its effective concentration is lower than that of melibiose. Lactulose and trehalose were applied individually to mice before a bilateral intrahippocampal CA1 injection of oligomeric Aβ_25-35. The administration of lactulose and trehalose attenuated the short-term memory and the learning retrieval of Alzheimer's disease (AD) mice. From a pathological analysis, we found that the pretreatment of lactulose and trehalose decreased neuroinflammation and increased the levels of the autophagic pathways. These results suggest that the neuroprotective effects of both lactulose and trehalose are achieved through anti-inflammation and autophagy. In addition, lactulose was better than trehalose in the enhancement of the synaptic protein expression level in AD mice. Therefore, lactulose could potentially be developed into a preventive and/or therapeutic disaccharide for AD.

"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.

Hydration of Carboxyl Groups: A Route toward Molecular Recognition?

On Earth, water plays an active role in cellular life, over several scales of distance and time. At a nanoscale, water drives macromolecular conformation through hydrophobic forces and at short times acts as a proton donor/acceptor providing charge carriers for signal transmission. At longer times and larger distances, water controls osmosis, transport, and protein mobility. Neutron diffraction experiments augmented by computer simulation, show that the three-dimensional shape of the hydration shell of carboxyl and carboxylate groups belonging to different molecules is characteristic of each molecule. Different hydration shells identify and distinguish specific sites with the same chemical structure. This experimental evidence suggests an active role of water also in controlling, modulating, and mediating chemical reactions involving carboxyl and carboxylate groups.

Trehalose Effect on the Aggregation of Model Proteins into Amyloid Fibrils

Protein aggregation into amyloid fibrils is a phenomenon that attracts attention from a wide and composite part of the scientific community. Indeed, the presence of mature fibrils is associated with several neurodegenerative diseases, and in addition these supramolecular aggregates are considered promising self-assembling nanomaterials. In this framework, investigation on the effect of cosolutes on protein propensity to aggregate into fibrils is receiving growing interest, and new insights on this aspect might represent valuable steps towards comprehension of highly complex biological processes. In this work we studied the influence exerted by the osmolyte trehalose on fibrillation of two model proteins, that is, lysozyme and insulin, investigated during concomitant variation of the solution ionic strength due to NaCl. In order to monitor both secondary structures and the overall tridimensional conformations, we have performed UV spectroscopy measurements with Congo Red, Circular Dichroism, and synchrotron Small Angle X-ray Scattering. For both proteins we describe the effect of trehalose in changing the fibrillation pattern and, as main result, we observe that ionic strength in solution is a key factor in determining trehalose efficiency in slowing down or blocking protein fibrillation. Ionic strength reveals to be a competitive element with respect to trehalose, being able to counteract its inhibiting effects toward amyloidogenesis. Reported data highlight the importance of combining studies carried out on cosolutes with valuation of other physiological parameters that may affect the aggregation process. Also, the obtained experimental results allow to hypothesize a plausible mechanism adopted by the osmolyte to preserve protein surface and prevent protein fibrillation.

The Roots of Plant Frost Hardiness and Tolerance

Frost stress severely affects agriculture and agroforestry worldwide. Although many studies about frost hardening and resistance have been published, most of them focused on the aboveground organs and only a minority specifically targets the roots. However, roots and aboveground tissues have different physiologies and stress response mechanisms. Climate models predict an increase in the magnitude and frequency of late-frost events, which, together with an observed loss of soil insulation, will greatly decrease plant primary production due to damage at the root level. Molecular and metabolic responses inducing root cold hardiness are complex. They involve a variety of processes related to modifications in cell wall composition, maintenance of the cellular homeostasis and the synthesis of primary and secondary metabolites. After a summary of the current climatic models, this review details the specificity of freezing stress at the root level and explores the strategies roots developed to cope with freezing stress. We then describe the level to which roots can be frost hardy, depending on their age, size category and species. After that, we compare the environmental signals inducing cold acclimation and frost hardening in the roots and aboveground organs. Subsequently, we discuss how roots sense cold at a cellular level and briefly describe the following signal transduction pathway, which leads to molecular and metabolic responses associated with frost hardening. Finally, the current options available to increase root frost tolerance are explored and promising lines of future research are discussed.

Influence of microwave-assisted dehydration on morphological integrity and viability of cat ovarian tissues: First steps toward long-term preservation of complex biomaterials at supra-zero temperatures

Ovarian tissue contains large pools of immature oocytes enclosed in primordial follicles, making it an attractive target for fertility preservation in female cancer patients, livestock and wild species. Compared to cryopreservation, desiccation and long-term storage of samples at supra-zero temperatures (using strategies inspired from small organisms to resist extreme environments) would be more cost-effective and convenient. The objective of the study was to characterize the influence of microwave-assisted dehydration on structural and functional properties of living ovarian tissues. While this method allows preservation of single cells (cat oocytes and sperm cells so far) using trehalose as the xeroprotectant, it has not been developed for multicellular tissues yet. Ovarian cortex biopsies were reversibly permeabilized, exposed to various concentrations of trehalose, and dried for different times using a commercial microwave under thermal control. Effective dehydration of samples along with proper trehalose retention were reached within 30 min of microwave drying. Importantly, the process did not affect morphology and DNA integrity of follicles or stromal cells. Moreover, transcriptional activity and survival of follicles were partially maintained following 10 min of drying, which already was compatible with storage at non-cryogenic temperatures. Present data provide critical foundation to develop dry-preservation techniques for long-term storage of living multicellular tissues.

Trehalose-functional glycopeptide enhances glycerol-free cryopreservation of red blood cells

Arginine- and trehalose-modified ε-polylysine (ε-PL) demonstrated a high synergistic function with trehalose for RBC cryopreservation.