Thermal inactivation of the plasma membrane H+-ATPase from Kluyveromyces lactis. Protection by trehalose

Isolation of the Sarcoplasmic Reticulum Ca2+-ATPase from Rabbit Fast-Twitch Muscle

The sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) is a membrane protein that is destabilized during purification in the absence of calcium ions. The disaccharide trehalose is a protein stabilizer that accumulates in the yeast cytoplasm when under stress. In the present work, SERCA was purified by including trehalose in the purification protocol. The purified SERCA showed high protein purity (~95%) and ATPase activity. ATP hydrolysis was dependent on the presence of Ca2+ and the enzyme kinetics showed a hyperbolic dependence on ATP (Km = 12.16 ± 2.25 μM ATP). FITC labeling showed the integrity of the ATP-binding site and the identity of the isolated enzyme as a P-type ATPase. Circular dichroism (CD) spectral changes at a wavelength of 225 nm were observed upon titration with ATP, indicating α-helical rearrangements in the nucleotide-binding domain (N-domain), which correlated with ATP affinity (Km). The presence of Ca2+ did not affect FITC labeling or the ATP-mediated structural changes at the N-domain. The use of trehalose in the SERCA purification protocol stabilized the enzyme. The isolated SERCA appears to be suitable for structural and ligand binding studies, e.g., for testing newly designed or natural inhibitors. The use of trehalose is recommended for the isolation of unstable enzymes.

Clinical validation of visual LAMP and qLAMP assays for the rapid detection of Toxoplasma gondii

Humans are exposed to Toxoplasma gondii infection as pet cats gradually become family members and represent an increasing public health risk worldwide. Toxoplasmosis diagnosis constitutes an important measure for disease prevention and control. In this study, real-time fluorescence quantitative loop-mediated isothermal amplification (qLAMP) and visual LAMP detection technologies were established to conduct tests of T. gondii based on the membrane DNA extraction method, and the optimal detection mix was determined by adding the protective reagent trehalose and screening the concentrations of Mg²⁺ and dNTPs. Paraffin and lyophilization were used to reduce and even remove aerosol pollution, constructing a detailed anti-contamination protocol. Based on the positive standard plasmid DNA, the LODs of qLAMP and visual LAMP were 92 copies/μL and 92 copies/μL, and the standard curve of qLAMP was Y=2.9503X+20.8992 with R^{2 =} 0.99. The applicability of the qLAMP and visual LAMP assays in disease diagnosis was assessed by evaluating 200 clinical cat faeces samples. The assays showed good diagnostic consistency, with kappa values of 1.0 and 0.99 compared with TaqMan qPCR, respectively. Compared with TaqMan qPCR, the diagnostic specificity/sensitivity of qLAMP and visual LAMP were 100%/100% and 100%/80%, respectively. The qLAMP and visual LAMP assays reported here are rapid and simple tests without extensive sample preparation and have a short turnaround time within 60 min, making them suitable for point-of-care testing.

Kramers’ Theory and the Dependence of Enzyme Dynamics on Trehalose-Mediated Viscosity

The disaccharide trehalose is accumulated in the cytoplasm of some organisms in response to harsh environmental conditions. Trehalose biosynthesis and accumulation are important for the survival of such organisms by protecting the structure and function of proteins and membranes. Trehalose affects the dynamics of proteins and water molecules in the bulk and the protein hydration shell. Enzyme catalysis and other processes dependent on protein dynamics are affected by the viscosity generated by trehalose, as described by the Kramers’ theory of rate reactions. Enzyme/protein stabilization by trehalose against thermal inactivation/unfolding is also explained by the viscosity mediated hindering of the thermally generated structural dynamics, as described by Kramers’ theory. The analysis of the relationship of viscosity–protein dynamics, and its effects on enzyme/protein function and other processes (thermal inactivation and unfolding/folding), is the focus of the present work regarding the disaccharide trehalose as the viscosity generating solute. Finally, trehalose is widely used (alone or in combination with other compounds) in the stabilization of enzymes in the laboratory and in biotechnological applications; hence, considering the effect of viscosity on catalysis and stability of enzymes may help to improve the results of trehalose in its diverse uses/applications.

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.

The Oligomeric State of the Plasma Membrane H⁺-ATPase from Kluyveromyces lactis

The plasma membrane H⁺-ATPase was purified from the yeast K. lactis. The oligomeric state of the H⁺-ATPase is not known. Size exclusion chromatography displayed two macromolecular assembly states (MASs) of different sizes for the solubilized enzyme. Blue native electrophoresis (BN-PAGE) showed the H⁺-ATPase hexamer in both MASs as the sole/main oligomeric state—in the aggregated and free state. The hexameric state was confirmed in dodecyl maltoside-treated plasma membranes by Western-Blot. Tetramers, dimers, and monomers were present in negligible amounts, thus depicting the oligomerization pathway with the dimer as the oligomerization unit. H⁺-ATPase kinetics was cooperative (n~1.9), and importantly, in both MASs significant differences were determined in intrinsic fluorescence intensity, nucleotide affinity and V_max; hence suggesting the large MAS as the activated state of the H⁺-ATPase. It is concluded that the quaternary structure of the H⁺-ATPase is the hexamer and that a relationship seems to exist between ATPase function and the aggregation state of the hexamer.

Trehalose Mediated Inhibition of Lactate Dehydrogenase from Rabbit Muscle. The Application of Kramers' Theory in Enzyme Catalysis

Lactate dehydrogenase (LDH) catalyzes the reduction of pyruvate to lactate by using NADH. LDH kinetics has been proposed to be dependent on the dynamics of a loop over the active site. Kramers' theory has been useful in the study of enzyme catalysis dependent on large structural dynamics. In this work, LDH kinetics was studied in the presence of trehalose and at different temperatures. In the absence of trehalose, temperature increase raised exponentially the LDH V_max and revealed a sigmoid transition of K_m toward a low-affinity state similar to protein unfolding. Notably, LDH V_max diminished when in the presence of trehalose, while pyruvate affinity increased and the temperature-mediated binding site transition was hindered. The effect of trehalose on k_cat was viscosity dependent as described by Kramers' theory since V_max correlated inversely with the viscosity of the medium. As a result, activation energy ( E_a) for pyruvate reduction was dramatically increased by trehalose presence. This work provides experimental evidence that the dynamics of a structural component in LDH is essential for catalysis, i.e., the closing of the loop on the active site. While the trehalose mediated-increased of pyruvate affinity is proposed to be due to the compaction and/or increase of structural order at the binding site.

Changing relations between proteins and osmolytes: a choice of nature

The stabilization and destabilization of the protein in the presence of any additive is mainly attributed to its preferential exclusion from protein surface and its preferential binding to the protein surface, respectively.

NMR study on the interaction of trehalose with lactose and its effect on the hydrogen bond interaction in lactose

Trehalose, a well-known stress-protector of biomolecules, has been investigated for its effect on the mobility, hydration and hydrogen bond interaction of lactose using diffusion-ordered NMR spectroscopy and NMR of hydroxy protons. In ternary mixtures of trehalose, lactose and water, the two sugars have the same rate of diffusion. The chemical shifts, temperature coefficients, vicinal coupling constants and ROE of the hydroxy protons in trehalose, lactose and sucrose were measured for the disaccharides alone in water/acetone-d₆ solutions as well as in mixtures. The data indicated that addition of trehalose did not change significantly the strength of the hydrogen bond interaction between GlcOH3 and GalO5' in lactose. Small upfield shifts were however measured for all hydroxy protons when the sugar concentration was increased. The chemical shift of the GlcOH3 signal in lactose showed less change, attributed to the spatial proximity to GalO5'. Chemical exchange between hydroxy protons of lactose and trehalose was observed in the ROESY NMR spectra. Similar effects were observed with sucrose indicating no specific effect of trehalose at the concentrations investigated (73 to 763 mg/mL) and suggesting that it is the concentration of hydroxy groups more than the type of sugars which is guiding intermolecular interactions.

Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Internal pH regulation is vital for many cell functions, including transport mechanisms and metabolic enzyme activity. More specifically, transport mechanisms are to a wide degree governed by internal pH distributions. We introduce the term standard deviation of the intracellular pH (s.d.(pH(int))) to describe the internal pH distributions. The cellular pH distributional response to external stress such as heat has not previously been determined. In this study, the intracellular pH (pH(i)) and the s.d.(pH(int)) of Saccharomyces cerevisiae cells exposed to supralethal temperatures were measured using fluorescence ratio imaging microscopy (FRIM). An exponential decline in pH(i) was observed after an initial small decline. For the first time, we report the use of FRIM for determining in vivo plasma membrane proton permeability coefficients in yeast. Furthermore, the exponential decay of pH(i) and the rupture of the cell plasma membrane, as measured by propidium iodide staining, at 70°C were not simultaneous but were separated by a significant temporal difference. Finally, a nonlinear relationship between the pH(i) and s.d.(pH(int)) was found; i.e. the s.d.(pH(int)) was significantly more sensitive to supralethal temperatures than pH(i). s.d.(pH(int)) is therefore proposed as an early health/vitality indicator in S. cerevisiae cells exposed to heat stress.

Kinetics of the thermal inactivation and aggregate formation of rabbit muscle pyruvate kinase in the presence of trehalose

In a previous study we found that 30-40% dimethylsulfoxide induces the active conformation of rabbit muscle pyruvate kinase. Because dimethylsulfoxide is known to perturb structure and function of many proteins, we have explored the effect of trehalose on the kinetics of thermal inactivation and stability of pyruvate kinase; this is because trehalose, in contrast to dimethyl sulfoxide, is totally excluded from the hydration shell of proteins. The results show that 600 mM trehalose inhibits the activity of pyruvate kinase by about 20% at 25 degrees C, however, trehalose protects pyruvate kinase from thermal inactivation at 60 degrees C, increases the Tm(app) of unfolding by 7.2 degrees C, induces a more compact state, and stabilizes its tetrameric structure. The inactivation process is irreversible due to the formation of protein aggregates. Trehalose diminishes the rate of formation of intermediates with propensity to aggregate, but does not affect the extent of aggregation. Remarkably, trehalose affects the aggregation process by inducing aggregates with amyloid-like characteristics.

Trehalose-mediated thermal stabilization of glucose oxidase from Aspergillus niger

Thermal inactivation and enzyme kinetics of glucose oxidase (a FAD dependent enzyme) were studied in the absence and presence of trehalose. The inactivation rate constant decreased by up to 50% at temperatures between 50 and 70 degrees C in the presence of 0.6M trehalose; as a consequence the glucose oxidase half-life increased. Intrinsic fluorescence spectra showed a maximum center of spectral mass (CSM) red shift of 6.5nm. Therefore, major structural changes seem to be related to glucose oxidase thermal inactivation. Trehalose decreased the rate constant for unfolding as monitored by CSM red shift kinetics indicating that this disaccharide favors the most compact folded state. The E(a) for unfolding was increased from 204 to 221kJ mol(-1). It is proposed that FAD dissociation is preceded by the exposition of hydrophobic regions, while the presence of trehalose was able to hinder the release of FAD. Enzyme kinetics analysis showed that trehalose does not affect V(max) but instead decreases K(m); as a result enzyme efficiency was increased. The stabilizing effect of trehalose in a cofactor-dependent enzyme has not been tested to date. In addition, glucose oxidase has an enormous commercial importance and therefore, the use of trehalose to stabilize glucose oxidase in its multiple applications seems to be promising.

Engineering and Directed Evolution of a Ca2+Binding Site A-Deficient AprE Mutant Reveal an Essential Contribution of the Loop Leu75–Leu82to Enzyme Activity

AnaprEmutant fromB. subtilis168 lacking the connecting loopLeu75–Leu82which is predicted to encode aCa2+binding site was constructed. Expression of the mutant gene (aprEΔLeu75–Leu82) producedB. subtiliscolonies lacking protease activity. Intrinsic fluorescence analysis revealed spectral differences between wild-type AprE and AprEΔL75–L82. An AprEΔL75–L82variant with reestablished enzyme activity was selected by directed evolution. The novel mutationsThr66Met/Gly102Asp located in positions which are predicted to be important for catalytic activity were identified in this variant. Although these mutations restored hydrolysis, they had no effect with respect to thermal inactivation of AprEΔL75–L82 T66M G102D. These results support the proposal that in addition to function as a calcium binding site, the loop that connectsβ-sheet e3 withα-helix c plays a structural role on enzyme activity of AprE fromB. subtilis168.

Fluorescence quenching by nucleotides of the plasma membrane H+-ATPase from Kluyveromyces lactis

The yeast plasma membrane H+-ATPase isolation procedure was improved; a highly pure enzyme (90-95%) was obtained after centrifugation on a trehalose concentration gradient. H+-ATPase kinetics was slightly cooperative: Hill number = 1.5, S0.5 = 800 microM ATP, and turnover number = 36 s-1. In contrast to those of other P-type ATPases, H+-ATPase fluorescence was highly sensitive to nucleotide binding; the fluorescence decreased 60% in the presence of both 5 mM ADP and AMP-PNP. Fluorescence titration with nucleotides allowed calculation of dissociation constants (Kd) from the binding site; Kd values for ATP and ADP were 700 and 800 microM, respectively. On the basis of amino acid sequence and homology model analysis, we propose that binding of the nucleotide to the N-domain is coupled to the movement of a loop beta structure and to the exposure of the Trp505 residue located in the loop. The recombinant N-domain also displayed a large hyperbolic fluorescence quenching when ATP binds; however, it displayed a higher affinity for ATP (Kd = 100 microM). We propose for P-type ATPases that structural movements during nucleotide binding could be followed if a Trp residue is properly located in the N-domain. Further, we propose the use of trehalose in enzyme purification protocols to increase the purity and quality of the isolated protein and to perform structural studies.

Opposing effects of two osmolytes ? trehalose and glycerol ? on thermal inactivation of rabbit muscle 6-phosphofructo-1-kinase

Trehalose and glycerol are known as good stabilizers of function and structure of several macromolecules against stress conditions. We previously reported that they have comparable effectiveness on protecting two yeast cytosolic enzymes against thermal inactivation. However, enzyme protection has always been associated to a decrease in catalytic activity at the stabilizing conditions i.e., the presence of the protective molecule. In the present study we tested trehalose and glycerol on thermal protection of the mammalian cytosolic enzyme phosphofructokinase. Here we found that trehalose was able to protect phosphofructokinase against thermal inactivation as well as to promote an activation of its catalytic activity. The enzyme incubated in the presence of 1 M trehalose did not present any significant inactivation within 2 h of incubation at 50 degrees C, contrasting to control experiments where the enzyme was fully inactivated during the same period exhibiting a t0.5 for thermal inactivation of 56+/-5 min. On the other hand, enzyme incubated in the presence of 37.5% (v/v) glycerol was not protected against incubation at 50 degrees C. Indeed, when phosphofructokinase was incubated for 45 min at 50 degrees C in the presence of lower concentrations of glycerol (7.5-25%, v/v), the remaining activity was 2-4 times lower than control. These data show that the compatibility of effects previously shown for trehalose and glycerol with some yeast cytosolic enzymes can not be extended to all globular enzyme system. In the case of phosphofructokinase, we believe that its property of shifting between several different complex oligomers configurations can be influenced by the physicochemical properties of the stabilizing molecules.

Trehalose-mediated inhibition of the plasma membrane H+-ATPase from Kluyveromyces lactis: dependence on viscosity and temperature

The effect of increasing trehalose concentrations on the kinetics of the plasma membrane H+-ATPase from Kluyveromyces lactis was studied at different temperatures. At 20 degrees C, increasing concentrations of trehalose (0.2 to 0.8 M) decreased V(max) and increased S(0.5) (substrate concentration when initial velocity equals 0.5 V(max)), mainly at high trehalose concentrations (0.6 to 0.8 M). The quotient V(max)/S(0.5) decreased from 5.76 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the absence of trehalose to 1.63 micromol of ATP mg of protein(-1) x min(-1) x mM(-1) in the presence of 0.8 M trehalose. The decrease in V(max) was linearly dependent on solution viscosity (eta), suggesting that inhibition was due to hindering of protein domain diffusional motion during catalysis and in accordance with Kramer's theory for reactions in solution. In this regard, two other viscosity-increasing agents, sucrose and glycerol, behaved similarly, exhibiting the same viscosity-enzyme inhibition correlation predicted. In the absence of trehalose, increasing the temperature up to 40 degrees C resulted in an exponential increase in V(max) and a decrease in enzyme cooperativity (n), while S(0.5) was not modified. As temperature increased, the effect of trehalose on V(max) decreased to become negligible at 40 degrees C, in good correlation with the temperature-mediated decrease in viscosity. The trehalose-mediated increase in S(0.5) was similar at all temperatures tested, and thus, trehalose effects on V(max)/S(0.5) were always observed. Trehalose increased the activation energy for ATP hydrolysis. Trehalose-mediated inhibition of enzymes may explain why yeast rapidly hydrolyzes trehalose when exiting heat shock.

Routine preparation of air-dried negatively stained and unstained specimens on holey carbon support films: a review of applications

Several representative examples are given of the successful application of negative staining across the holes of holey carbon support films using 5% (w/v) ammonium molybdate solution containing trehalose. The inclusion of 0.1% (w/v) trehalose is considered to be most satisfactory, although good data have also been obtained in the presence of 0.01 and 1.0% (w/v) trehalose. The examples given fall into the following groups: protein molecules in the absence of polyethylene glycol (PEG), protein molecules in the presence of PEG (Mr 1000), lipoproteins, lipids and membranes, filaments and tubules, viruses in the absence of PEG, viruses in the presence of PEG, aqueous polymer solutions, and finally for comparison purposes, four unstained samples studied in the presence of trehalose alone. In all these cases, and many others not documented here, successful spreading of the sample across holes has been achieved, with the sample embedded within a thin film of air-dried ammonium molybdate+trehalose. These specimens can be rapidly produced and provide an alternative to negatively stained specimens on carbon support films. Specimen stability in the electron bean is good and such specimens can usually generate superior negatively stained TEM images without flattening and adsorption artefacts. The formation of 2-D arrays/crystals of protein molecules and viruses, suspended across holes in the presence of ammonium molbybdate+trehalose, and trehalose alone, is also demonstrated.

The trehalose myth revisited: introduction to a symposium on stabilization of cells in the dry state

This essay is an introduction to a series of papers arising from a symposium on stabilization of cells in the dry state. Nearly all of these investigations have utilized the sugar trehalose as a stabilizing molecule. Over the past two decades a myth has grown up about special properties of trehalose for stabilization of biomaterials. We review many of such uses here and show that under ideal conditions for drying and storage trehalose has few, if any, special properties. However, under suboptimal conditions trehalose has some distinct advantages and thus may remain the preferred excipient. We review the available mechanisms for introducing trehalose into the cytoplasm of living cells as an introduction to the papers that follow.