Unfolding and aggregation during the thermal denaturation of streptokinase

SEM Observation of the Filter after Administration of Blinatumomab: A Possibility of Leakage during Home Administration Using a Portable Infusion Pump

Blinatumomab (Blincyto® injection solution) is classified as a bispecific T-cell engaging (BiTE) antibody and is intended for the treatment of relapsed/refractory acute lymphoblastic leukemia. It requires continuous infusion to maintain therapeutic levels. Therefore, it is often administered at home. Monoclonal antibodies, which are administered intravenously, have the potential to leak depending on the nature of the administration devices. Therefore, we investigated device-associated causes of blinatumomab leakage. We observed no apparent changes to the filter and its materials after exposure to the injection solution and surfactant. From scanning electron microscopic images, precipitate on the surface of the filters was observed after physical stimulation of the injection solution. Therefore, physical stimulations should be avoided during the prolonged administration of blinatumomab. In conclusion, the findings of this study assist in the safe administration of antibodies using portable infusion pumps, taking into consideration the composition of drug excipients and the choice of filter type and structure.

Nonspecific Amyloid Aggregation of Chicken Smooth-Muscle Titin: In Vitro Investigations

A giant multidomain protein of striated and smooth vertebrate muscles, titin, consists of tandems of immunoglobulin (Ig)- and fibronectin type III (FnIII)-like domains representing β-sandwiches, as well as of disordered segments. Chicken smooth muscles express several titin isoforms of ~500-1500 kDa. Using various structural-analysis methods, we investigated in vitro nonspecific amyloid aggregation of the high-molecular-weight isoform of chicken smooth-muscle titin (SMT_HMW, ~1500 kDa). As confirmed by X-ray diffraction analysis, under near-physiological conditions, the protein formed amorphous amyloid aggregates with a quaternary cross-β structure within a relatively short time (~60 min). As shown by circular dichroism and Fourier-transform infrared spectroscopy, the quaternary cross-β structure-unlike other amyloidogenic proteins-formed without changes in the SMT_HMW secondary structure. SMT_HMW aggregates partially disaggregated upon increasing the ionic strength above the physiological level. Based on the data obtained, it is not the complete protein but its particular domains/segments that are likely involved in the formation of intermolecular interactions during SMT_HMW amyloid aggregation. The discovered properties of titin position this protein as an object of interest for studying amyloid aggregation in vitro and expanding our views of the fundamentals of amyloidogenesis.

Ion-Mediated Morphological Diversity in Protein Amyloid Systems

Salt ions are considered among the major determinants ruling protein folding, stability, and self-assembly in the context of amyloid-related diseases, protein drug development, and functional biomaterials. Here, we report that Hofmeister ions not only determine the rate constants of the aggregation reaction for human insulin and hen egg white lysozyme but also control the generation of a plethora of amyloid-like morphologies ranging from the nanoscale to the microscale. We anticipate that the latter is a result of a balance between colloidal and conformational stability combined with an ion-specific effect and highlight the importance of salt ions in controlling the biological functions of protein aggregates.

Distinct populations of highly potent TAU seed conformers in rapidly progressing Alzheimer's disease

[Figure: see text].

(Macro)Molecular Imprinting of Proteins on PCL Electrospun Scaffolds

Biological recognition sites are very useful for biomedical purposes and, more specifically, for polymeric scaffolds. However, synthetic polymers are not capable of providing specific biological recognition sites. To solve this inconvenience, functionalization of biological moieties is typically performed, oftentimes via peptide binding. In this sense, the main task is capturing the biological complexity of a protein. This study proposes a possible alternative solution to this challenge. Our approach is based on the combination of molecular imprinting (MI) and electrospinning processes. We propose here an alternative MI approach with polymeric structures, instead of using cross-linkers and monomers as conventionally performed. Different PCL-protein scaffolds were produced via electrospinning before performing MI. Gelatin, collagen, and elastin were used as proteins. Results evidenced that the MI process conducted with PCL electrospun membranes was carried out with ionic interactions between the desired molecules and the recognition sites formed. In addition, it has been proved that MI was more efficient when using gelatin as a template. This approach opens a new stage in the development of recognition sites in scaffolds obtained with synthetic polymers and their application for biomedical purposes.

Diverse, evolving conformer populations drive distinct phenotypes in frontotemporal lobar degeneration caused by the same MAPT-P301L mutation

Tau protein accumulation is a common denominator of major dementias, but this process is inhomogeneous, even when triggered by the same germline mutation. We considered stochastic misfolding of human tau conformers followed by templated conversion of native monomers as an underlying mechanism and derived sensitive conformational assays to test this concept. Assessments of brains from aged TgTauP301L transgenic mice revealed a prodromal state and three distinct signatures for misfolded tau. Frontotemporal lobar degeneration (FTLD)-MAPT-P301L patients with different clinical phenotypes also displayed three signatures, two resembling those found in TgTauP301L mice. As physicochemical and cell bioassays confirmed diverse tau strains in the mouse and human brain series, we conclude that evolution of diverse tau conformers is intrinsic to the pathogenesis of this uni-allelic form of tauopathy. In turn, effective therapeutic interventions in FTLD will need to address evolving repertoires of misfolded tau species rather than singular, static molecular targets.

Lipid modification of staphylokinase and its implications on stability and activity

Thrombolytic agents are routinely used to dissolve blood clot by activating fibrinolytic system. Among different thrombolytic agents available, staphylokinase (SAK) is gaining much attention because of their fibrin specificity and reduced inhibition by α2 antiplasmin. Though SAK had exhibited less circulatory half life, they are equipotent to tissue plasminogen activator and streptokinase and had shown more potency for clot dissolution during retracted thrombi. In this study, SAK was lipid modified at the N-terminal by a protein engineering approach to enhance its stability and activity. Native SAK as well as the gene encoding SAK with lipobox was cloned into E. coli GJ1158 using pRSET-B expression vector for higher expression. The lipid modification of SAK was confirmed by a mobility shift of 1.3 kDa against the 15.5 kDa of native SAK using tricine SDS-PAGE. Lipid modification of SAK was confirmed by LC MS/MS. The secondary structure analysis was carried out using circular dichroism and deconvoluted fourier transform infrared spectroscopy. LMSAK was found to have a slightly higher denaturation temperature compared to SAK. The improved stablility and activity of lipid modified SAK was studied by heated plasma agar plate assay and mouse tail bleeding test.

Neurodegenerative Diseases: Regenerative Mechanisms and Novel Therapeutic Approaches

Regeneration refers to regrowth of tissue in the central nervous system. It includes generation of new neurons, glia, myelin, and synapses, as well as the regaining of essential functions: sensory, motor, emotional and cognitive abilities. Unfortunately, regeneration within the nervous system is very slow compared to other body systems. This relative slowness is attributed to increased vulnerability to irreversible cellular insults and the loss of function due to the very long lifespan of neurons, the stretch of cells and cytoplasm over several dozens of inches throughout the body, insufficiency of the tissue-level waste removal system, and minimal neural cell proliferation/self-renewal capacity. In this context, the current review summarized the most common features of major neurodegenerative disorders; their causes and consequences and proposed novel therapeutic approaches.

YhjA - An Escherichia coli trihemic enzyme with quinol peroxidase activity

The trihemic bacterial cytochrome c peroxidase from Escherichia coli, YhjA, is a membrane-anchored protein with a C-terminal domain homologous to the classical bacterial peroxidases and an additional N-terminal (NT) heme binding domain. Recombinant YhjA is a 50 kDa monomer in solution with three c-type hemes covalently bound. Here is reported the first biochemical and spectroscopic characterization of YhjA and of the NT domain demonstrating that NT heme is His63/Met125 coordinated. The reduction potentials of P (active site), NT and E hemes were established to be -170 mV, +133 mV and +210 mV, respectively, at pH 7.5. YhjA has quinol peroxidase activity in vitro with optimum activity at pH 7.0 and millimolar range K_M values using hydroquinone and menadiol (a menaquinol analogue) as electron donors (K_M = 0.6 ± 0.2 and 1.8 ± 0.5 mM H₂O₂, respectively), with similar turnover numbers (k_cat = 19 ± 2 and 13 ± 2 s^-1, respectively). YhjA does not require reductive activation for maximum activity, in opposition to classical bacterial peroxidases, as P heme is always high-spin 6-coordinated with a water-derived molecule as distal axial ligand but shares the need for the presence of calcium ions in the kinetic assays. Formation of a ferryl Fe(IV) = O species was observed upon incubation of fully oxidized YhjA with H₂O₂. The data reported improve our understanding of the biochemical properties and catalytic mechanism of YhjA, a three-heme peroxidase that uses the quinol pool to defend the cells against hydrogen peroxide during transient exposure to oxygenated environments.

External cavity-quantum cascade laser infrared spectroscopy for secondary structure analysis of proteins at low concentrations

Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy are analytical techniques employed for the analysis of protein secondary structure. The use of CD spectroscopy is limited to low protein concentrations (<2 mg ml(-1)), while FTIR spectroscopy is commonly used in a higher concentration range (>5 mg ml(-1)). Here we introduce a quantum cascade laser (QCL)-based IR transmission setup for analysis of protein and polypeptide secondary structure at concentrations as low as 0.25 mg ml(-1) in deuterated buffer solution. We present dynamic QCL-IR spectra of the temperature-induced α-helix to β-sheet transition of poly-L-lysine. The concentration dependence of the α-β transition temperature between 0.25 and 10 mg ml(-1) was investigated by QCL-IR, FTIR and CD spectroscopy. By using QCL-IR spectroscopy it is possible to perform IR spectroscopic analysis in the same concentration range as CD spectroscopy, thus enabling a combined analysis of biomolecules secondary structure by CD and IR spectroscopy.

Longevity of animals under reactive oxygen species stress and disease susceptibility due to global warming

The world is projected to experience an approximate doubling of atmospheric CO₂ concentration in the next decades. Rise in atmospheric CO₂ level as one of the most important reasons is expected to contribute to raise the mean global temperature 1.4 °C-5.8 °C by that time. A survey from 128 countries speculates that global warming is primarily due to increase in atmospheric CO₂ level that is produced mainly by anthropogenic activities. Exposure of animals to high environmental temperatures is mostly accompanied by unwanted acceleration of certain biochemical pathways in their cells. One of such examples is augmentation in generation of reactive oxygen species (ROS) and subsequent increase in oxidation of lipids, proteins and nucleic acids by ROS. Increase in oxidation of biomolecules leads to a state called as oxidative stress (OS). Finally, the increase in OS condition induces abnormality in physiology of animals under elevated temperature. Exposure of animals to rise in habitat temperature is found to boost the metabolism of animals and a very strong and positive correlation exists between metabolism and levels of ROS and OS. Continuous induction of OS is negatively correlated with survivability and longevity and positively correlated with ageing in animals. Thus, it can be predicted that continuous exposure of animals to acute or gradual rise in habitat temperature due to global warming may induce OS, reduced survivability and longevity in animals in general and poikilotherms in particular. A positive correlation between metabolism and temperature in general and altered O₂ consumption at elevated temperature in particular could also increase the risk of experiencing OS in homeotherms. Effects of global warming on longevity of animals through increased risk of protein misfolding and disease susceptibility due to OS as the cause or effects or both also cannot be ignored. Therefore, understanding the physiological impacts of global warming in relation to longevity of animals will become very crucial challenge to biologists of the present millennium.

Aggregation Kinetics for IgG1-Based Monoclonal Antibody Therapeutics

Monoclonal antibodies (mAbs) as a class of therapeutic molecules are finding an increasing demand in the biotechnology industry for the treatment of diseases like cancer and multiple sclerosis. A key challenge associated to successful commercialization of mAbs is that from the various physical and chemical instabilities that are inherent to these molecules. Out of all probable instabilities, aggregation of mAbs has been a major problem that has been associated with a change in the protein structure and is a hurdle in various upstream and downstream processes. It can stimulate immune response causing protein misfolding having deleterious and harmful effects inside a cell. Also, the extra cost incurred to remove aggregated mAbs from the rest of the batch is huge. Size exclusion chromatography (SEC) is a major technique for characterizing aggregation in mAbs where change in the aggregates' size over time is estimated. The current project is an attempt to understand the rate and mechanism of formation of higher order oligomers when subjected to different environmental conditions such as buffer type, temperature, pH, and salt concentration. The results will be useful in avoiding the product exposure to conditions that can induce aggregation during upstream, downstream, and storage process. Extended Lumry-Eyring model (ELE), Lumry-Eyring Native Polymerization model (LENP), and Finke-Watzky model (F-W) have been employed in this work to fit the aggregation experimental data and results are compared to find the best fit model for mAb aggregation to connect the theoretical dots with the reality.

Liposomal nanocarriers for plasminogen activators

Several plasminogen activators (PAs) have been found effective in treating different thromboembolic diseases. However, administration of conventional thrombolytic therapy is limited by a low efficacy of present formulations of PAs. Conventional treatments using these therapeutic proteins are associated with several limitations including rapid inactivation and clearance, short half-life, bleeding complications or non-specific tissue targeting. Liposome-based formulations of PAs such as streptokinase, tissue-plasminogen activator and urokinase have been developed to improve the therapeutic efficacy of these proteins. Resulting liposomal formulations were found to preserve the original activity of PAs, promote their selective delivery and improve thrombus targeting. Therapeutic potential of these liposome-based PAs has been demonstrated successfully in various pre-clinical models in vivo. Reductions in unwanted side effects (e.g., hemorrhage or immunogenicity) as well as enhancements of efficacy and safety were achieved in comparison to currently existing treatment options based on conventional formulations of PAs. This review summarizes present achievements in: (i) preparation of liposome-based formulations of various PAs, (ii) development of PEGylated and targeted liposomal PAs, (iii) physico-chemical characterization of these developed systems, and (iv) testing of their thrombolytic efficacy. We also look to the future and the imminent arrival of theranostic liposomal formulations to move this field forward.

Charge and charge-pair mutations alter the rate of assembly and structural properties of apolipoprotein C-II amyloid fibrils

The misfolding, aggregation, and accumulation of proteins as amyloid fibrils is a defining characteristic of several debilitating diseases. Human apolipoprotein C-II (apoC-II) amyloid fibrils are representative of the fibrils formed by a number of plasma apolipoproteins implicated in amyloid-related disease. Previous structural analyses identified a buried charge pair between residues K30 and D69 within apoC-II amyloid fibrils. We have investigated the effects of amino acid substitutions of these residues on apoC-II fibril formation. Two point mutations of apoC-II, D69K and K30D, as well as a reversed ion-pair mutant containing both mutations (KDDK) were generated. Fibril formation by the double mutant, apoC-II KDDK, and apoC-II D69K was enhanced compared to that of wild-type (WT) apoC-II, while apoC-II K30D lacked the ability to form fibrils under standard conditions. Structural analyses showed that WT apoC-II, apoC-II D69K, and apoC-II KDDK fibrils have similar secondary structures and morphologies. Size distribution analyses revealed that apoC-II D69K fibrils have a broader range of fibril sizes while apoC-II KDDK fibrils showed an increased frequency of closed fibrillar loops. ApoC-II D69K fibrils exhibited reduced thioflavin T binding capacity compared to that of fibrils formed by WT apoC-II and apoC-II KDDK. These results indicate that specific charge and charge-pair mutations within apoC-II significantly alter the ability to form fibrils and that position 69 within apoC-II plays a key role in the rate-limiting step of apoC-II fibril formation.

Activity assessment of microbial fibrinolytic enzymes

Conversion of fibrinogen to fibrin inside blood vessels results in thrombosis, leading to myocardial infarction and other cardiovascular diseases. In general, there are four therapy options: surgical operation, intake of antiplatelets, anticoagulants, or fibrinolytic enzymes. Microbial fibrinolytic enzymes have attracted much more attention than typical thrombolytic agents because of the expensive prices and the side effects of the latter. The fibrinolytic enzymes were successively discovered from different microorganisms, the most important among which is the genus Bacillus. Microbial fibrinolytic enzymes, especially those from food-grade microorganisms, have the potential to be developed as functional food additives and drugs to prevent or cure thrombosis and other related diseases. There are several assay methods for these enzymes; this may due to the insolubility of substrate, fibrin. Existing assay methods can be divided into three major groups. The first group consists of assay of fibrinolytic activity with natural proteins as substrates, e.g., fibrin plate methods. The second and third groups of assays are suitable for kinetic studies and are based on the determination of hydrolysis of synthetic peptide esters. This review will deal primarily with the microorganisms that have been reported in literature to produce fibrinolytic enzymes and the first review discussing the methods used to assay the fibrinolytic activity.

Application and use of differential scanning calorimetry in studies of thermal fluctuation associated with amyloid fibril formation

The aggregation of proteins into amyloid fibrils is a topic that has attracted great interest because the process is associated with the pathology of numerous human diseases. Despite considerable progress in the elucidation of the structure of amyloid fibrils and the kinetic mechanism of their formation, knowledge on the thermodynamic aspects underlying the formation and stability of amyloid fibrils is limited. In this review, we summarize recent calorimetric studies of amyloid fibril formation, with the goal of obtaining a better understanding of the causal factors that thermally induce proteins to aggregate into amyloid fibrils. Calorimetric data show that differential scanning calorimetry is a useful technique to study the causative factors that thermally trigger the conversion to the amyloid structure and highlight the physics related to the thermal fluctuation of proteins during this conversion.

Shear flow induced changes in apolipoprotein C-II conformation and amyloid fibril formation

The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s(-1)) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5-10-fold. Fibrils produced at shear rates of 150 and 300 s(-1) were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s(-1), tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 μg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan residue in apoC-II as the donor and covalently attached acceptors showed that shear flow increased the distance between the donor and acceptor molecules. Shear-induced higher-order oligomeric species were identified by sedimentation velocity experiments using fluorescence detection, while fibril seeding experiments showed that species formed during shear flow are on the fibril formation pathway. These studies suggest that physiological shear flow conditions and conditions experienced during protein manufacturing can exert significant effects on protein conformation, leading to protein misfolding, aggregation, and amyloid fibril formation.

The use of native cation-exchange chromatography to study aggregation and phase separation of monoclonal antibodies

This study introduces a novel analytical approach for studying aggregation and phase separation of monoclonal antibodies (mAbs). The approach is based on using analytical scale cation-exchange chromatography (CEX) for measuring the loss of soluble monomer in the case of individual and mixed protein solutions. Native CEX outperforms traditional size-exclusion chromatography in separating complex protein mixtures, offering an easy way to assess mAb aggregation propensity. Different IgG1 and IgG2 molecules were tested individually and in mixtures consisting of up to four protein molecules. Antibody aggregation was induced by four different stress factors: high temperature, low pH, addition of fatty acids, and rigorous agitation. The extent of aggregation was determined from the amount of monomeric protein remaining in solution after stress. Consequently, it was possible to address the role of specific mAb regions in antibody aggregation by co-incubating Fab and Fc fragments with their respective full-length molecules. Our results revealed that the relative contribution of Fab and Fc regions in mAb aggregation is strongly dependent on pH and the stress factor applied. In addition, the CEX-based approach was used to study reversible protein precipitation due to phase separation, which demonstrated its use for a broader range of protein-protein association phenomena. In all cases, the role of Fab and Fc was clearly dissected, providing important information for engineering more stable mAb-based therapeutics.

Streptokinase loading in liposomes for vascular targeted nanomedicine applications: encapsulation efficiency and effects of processing

Vascular diseases leading to thrombo-occlusion are the leading cause of morbidity and mortality worldwide. Revascularization and restoration of antegrade blood flow is critical for tissue survival and patient health. In this aspect, systemic administration of thrombolytics (e.g., streptokinase) to dissolve occlusive thrombi is a clinically established strategy. However, this strategy typically necessitates the administration of large doses, leading to a high incidence of hemorrhagic complications due to systemic side effects. To minimize this risk, liposomes specifically targeted to the site of thrombo-occlusion have been bioengineered by exploiting ligand-receptor relationships pertinent to thrombus-associated cell phenotypes. This study focuses on encapsulating streptokinase within these liposomes, specifically regarding the effect of liposome processing conditions on streptokinase encapsulation and activity. Theoretical calculations of encapsulation capacity agreed well with that reported in the literature. The experimental encapsulation efficiency values are 45.9 ± 34.0% (n = 9 ± SD) and 21.6 ± 30.0% (n = 6 ± SD), using two different methods. The liposome processing conditions are found to decrease streptokinase activity; however, over 30% remain active after processing, maintaining enough activity to be therapeutic especially when protected inside a vehicle targeted to the site of thrombo-occlusion. The insight gained from the research reported here would enable refining the design and the processing conditions of liposomal formulations of fibrinolytics to yield reduced variability in encapsulation efficiency and streptokinase activity. The design of a thrombus-targeted 'stealth' liposome reported earlier and the current findings of fibrinolytics' encapsulation and activity in such liposomes can be efficiently integrated to develop an efficient strategy for vascular nanomedicine.

Physical instability of a therapeutic Fc fusion protein: domain contributions to conformational and colloidal stability

Protein therapeutics made up of artificially combined proteins or protein domains, so-called fusion proteins, are a novel and growing class of biopharmaceuticals. We have studied abatacept (Orencia), a fusion protein that is constructed of a modified IgG Fc domain and the soluble part of the T-cell receptor CTLA-4. In accelerated degradation studies conducted at 40 degrees C, a pH shift from 7.5 to 6.0 yields significantly faster aggregation kinetics, as measured by size-exclusion chromatography. To understand how the fusion domains and their interactions contribute to this result, we considered aggregation in light of the modified Lumry-Eyring reaction pathway. Protein conformational stabilities against chaotropes and temperature were measured. The structural consequences of these perturbations were observed by a variety of experimental techniques, including differential scanning calorimetry, circular dichroism, and intrinsic fluorescence. Abatacept's colloidal stability was studied by measuring zeta potentials and osmotic second virial coefficients, as well as by modeling electrostatic potentials on the protein's surface. The domains of abatacept exhibit different conformational stabilities that are highly pH dependent, whereas abatacept was weakly colloidally unstable at pH 6 or 7.5. These results are ascribed to conformational instability of the CTLA-4 and C(H)2 domains, which unfold to form a molten globule-like structure that is aggregation-prone. We suggest the instability against aggregation is determined by the least stable domains.

Theoretical and experimental investigation of chaperone effects on soluble recombinant proteins in Escherichia coli: effect of free DnaK level on temperature-induced recombinant streptokinase production

Modeling and analysis of genetic networks have become increasingly important in the investigation of cellular processes. The genetic networks involved in cellular stress response can have a critical effect on the productivity of recombinant proteins. In this work, it was found that the temperature-inducible expression system for the production of soluble recombinant streptokinase in Escherichia coli resulted in a lower productivity compared to the chemically-induced system. To investigate the effect of the induced cellular response due to temperature up-shift a model-based approach is adopted. The role played by the major molecular chaperone teams DnaK–DnaJ–GrpE and GroEL–GroES on the productivity of recombinant streptokinase was experimentally determined. Based on these investigations, a detailed mechanistic mathematical model was developed for the cellular response during the temperature-induced recombinant streptokinase production. The model simulations were found to have a good qualitative agreement with the experimental results. The mechanistic mathematical model was validated with the experiments conducted on a σ³² mutant strain. Detailed analysis of the parameter sensitivities of the model indicated that the level of free DnaK chaperone in the cell has the major effect on the productivity of recombinant streptokinase during temperature induction. Analysis of the model simulations also shows that down regulation or selective redirection of the heat shock proteins could be a better way of manipulating the cellular stress response than overexpression or deletion. In other words, manipulating the system properties resulting from the interaction of the components is better than manipulating the individual components. Although our results are specific to a recombinant protein (streptokinase) and the expression system (E. coli), we believe that such a systems-biological approach has several advantages over conventional experimental approaches and could be in principle extended to bigger genetic networks as well as other recombinant proteins and expression systems.

Poly Lactic Acid Based Injectable Delivery Systems for Controlled Release of a Model Protein, Lysozyme

The objective of this study was to evaluate the critical formulation parameters (i.e., polymer concentration, polymer molecular weight, and solvent nature) affecting the controlled delivery of a model protein, lysozyme, from injectable polymeric implants. The conformational stability and biological activity of the released lysozyme were also investigated. Three formulations containing 10%, 20%, and 30% (w/v) poly lactic acid (PLA) in triacetin were investigated. It was found that increasing polymer concentration in the formulations led to a lower burst effect and a slower release rate. Formulation with a high molecular weight polymer showed a greater burst effect as compared to those containing low molecular weight. Conformational stability and biological activity of released samples were studied by differential scanning calorimeter and enzyme activity assay, respectively. The released samples had significantly (P < 0.05) greater conformational stability and biological activity in comparison to the control (lysozyme in buffer solution kept at same conditions). Increasing polymer concentration increased both the conformational stability and the biological activity of released lysozyme. In conclusion, phase sensitive polymer-based delivery systems were able to deliver a model protein, lysozyme, in a conformationally stable and biologically active form at a controlled rate over an extended period.

Molecular and cellular aspects of protein misfolding and disease

Proteins are essential elements for life. They are building blocks of all organisms and the operators of cellular functions. Humans produce a repertoire of at least 30,000 different proteins, each with a different role. Each protein has its own unique sequence and shape (native conformation) to fulfill its specific function. The appearance of incorrectly shaped (misfolded) proteins occurs on exposure to environmental changes. Protein misfolding and the subsequent aggregation is associated with various, often highly debilitating, diseases for which no sufficient cure is available yet. In the first part of this review we summarize the structural composition of proteins and the current knowledge of underlying forces that lead proteins to lose their native structure. In the second and third parts we describe the molecular and cellular mechanisms that are associated with protein misfolding in disease. Finally, in the last part we portray recent efforts to develop treatments for protein misfolding diseases.

Thermodynamic and kinetic stability of penicillin acylase from Escherichia coli

Thermal denaturation of penicillin acylase (PA) from Escherichia coli has been studied by high-sensitivity differential scanning calorimetry as a function of heating rate, pH and urea concentration. It is shown to be irreversible and kinetically controlled. Upon decrease in the heating rate from 2 to 0.1 K min(-1) the denaturation temperature of PA at pH 6.0 decreases by about 6 degrees C, while the denaturation enthalpy does not change notably giving an average value of 31.6+/-2.1 J g(-1). The denaturation temperature of PA reaches a maximum value of 64.5 degrees C at pH 6.0 and decreases by about of 15 degrees C at pH 3.0 and 9.5. The pH induced changes in the denaturation enthalpy follow changes in the denaturation temperature. Increasing the urea concentration causes a decrease in both denaturation temperature and enthalpy of PA, where denaturation temperature obeys a linear relation. The heat capacity increment of PA is not sensitive to the heating rate, nor to pH, and neither to urea. Its average value is of 0.58+/-0.02 J g(-1) K(-1). The denaturation transition of PA is approximated by the Lumry-Eyring model. The first stage of the process is assumed to be a reversible unfolding of the alpha-subunit. It activates the second stage involving dissociation of two subunits and subsequent denaturation of the beta-subunit. This stage is irreversible and kinetically controlled. Using this model the temperature, enthalpy and free energy of unfolding of the alpha-subunit, and a rate constant of the irreversible stage are determined as a function of pH and urea concentration. Structural features of the folded and unfolded conformation of the alpha-subunit as well as of the transition state of the PA denaturation in aqueous and urea solutions are discussed.

Heat-Triggered Conversion of Protofibrils into Mature Amyloid Fibrils of β2-Microglobulin†

Heat-triggered conversion of the salt-induced thin and flexible protofibrils into well-organized thick and straight mature amyloid fibrils was achieved with beta2-microglobulin, a protein responsible for dialysis-related amyloidosis. First, protofibrils that formed spontaneously at pH 2.5 in the presence of 0.5 M NaCl were aggregated by agitating the solution. Second, the aggregated protofibrils were heated in a cell of a differential scanning calorimeter (DSC). The DSC thermogram showed an exothermic transition with sigmoidal temperature dependence, resulting in a remarkably large decrease in the heat capacity of the solution. Third, on the basis of electron microscopy together with circular dichroism spectroscopy, seeding experiments, and a thioflavin T binding assay, the sigmoidal transition was found to represent the conversion of protofibrils into mature amyloid fibrils. Furthermore, DSC thermograms obtained at various heating rates revealed that the transition curve depends on the heating rate, implying that the effects of heat associated with the conversion to the mature fibrils are kinetically controlled, precluding an interpretation in terms of equilibrium thermodynamics. Taken together, these results highlight the importance of the change in heat capacity in addressing the biological significance of interactions between solvent water and amyloid fibrils and, moreover, in detecting the formation of amyloid fibrils.

Analysis of sugar bioprotective mechanisms on the thermal denaturation of lysozyme from Raman scattering and differential scanning calorimetry investigations

Sugar-induced thermostabilization of lysozyme was analyzed by Raman scattering and modulated differential scanning calorimetry investigations, for three disaccharides (maltose, sucrose, and trehalose) characterized by the same chemical formula (C(12)H(22)O(11)). This study shows that trehalose is the most effective in stabilizing the folded secondary structure of the protein. The influence of sugars on the mechanism of thermal denaturation was carefully investigated by Raman scattering experiments carried out both in the low-frequency range and in the amide I band region. It was determined that the thermal stability of the hydrogen-bond network of water, highly dependent on the presence of sugars, contributes to the stabilization of the native tertiary structure and inhibits the first stage of denaturation, that is, the transformation of the tertiary structure into a highly flexible state with intact secondary structure. It was found that trehalose exhibits exceptional capabilities to distort the tetra-bonded hydrogen-bond network of water and to strengthen intermolecular O-H interactions responsible for the stability of the tertiary structure. Trehalose was also observed to be the best stabilizer of the folded secondary structure, in the transient tertiary structure, leading to a high-temperature shift of the unfolding process (the second stage of denaturation). This was interpreted from the consideration that the transient tertiary structure is less flexible and inhibits the solvent accessibility around the hydrophobic groups of lysozyme.

Streptokinase—the drug of choice for thrombolytic therapy

Thrombosis, the blockage of blood vessels with clots, can lead to acute myocardial infarction and ischemic stroke, both leading causes of death. Other than surgical interventions to remove or by pass the blockage, or the generation of collateral vessels to provide a new blood supply, the only treatment available is the administration of thrombolytic agents to dissolve the blood clot. This article describes a comprehensive review of streptokinase (SK). We discuss the biochemistry and molecular biology of SK, describing the mechanism of action, structures, confirmational properties, immunogenecity, chemical modification, and cloning and expression. The production and physico-chemical properties of this SK are also discussed. In this review, considering the properties and characteristics of SK that make it the drug of choice for thrombolytic therapy.

Real-time observation of temperature-dependent protein–protein interactions using real-time dual-color detection system

This study examined the ability of a real-time dual-color detection system to allow direct observations of the kinetics of temperature-dependent protein-protein interaction at a single-molecule level. The primary target protein was an Alexa Fluor 488-labeled actin conjugate, which had been pre-incubated with an unlabeled rabbit anti-actin antibody (IgG). The complementary fluorescent protein was Alexa Fluor 633-labeled goat anti-rabbit IgG antibody, which interacts with the rabbit anti-actin antibody (IgG) bound to the Alexa Fluor 488-labeled actin conjugate. The individual protein molecules labeled with different fluorescent dyes in solution were effectively focused, interacted with the other protein molecules at 500 aM, and detected directly in real-time using the dual-wavelength (lambda(ex)=488 and 635 nm) laser-induced fluorescence detection system. The kinetics of the protein-protein interactions were examined at different temperatures (12-32 degrees C). At concentrations in the aM range, the number of bound complex molecules through the protein-protein interaction decreased gradually with time at a given temperature, and increased with decreasing temperature at a set time. A high concentration (above 500 pM) of the protein sample caused aggregation and nonspecific binding of the protein molecules, even though the protein molecules were not an example of complementary binding. The results demonstrated that the real-time kinetics of a protein-protein interaction could be analyzed effectively at the single-molecule level without any time delay using the real-time dual-color detection system.

Aggregation kinetics of recombinant human FVIII (rFVIII)

The physical phenomenon of aggregation can have profound impact on the stability of therapeutic proteins. This study focuses on the aggregation behavior of recombinant human FVIII (rFVIII), a multi-domain protein used as the first line of therapy for hemophilia A, a bleeding disorder caused by the deficiency or dysfunction of factor VIII (FVIII). Thermal denaturation of rFVIII was investigated using circular dichroism (CD) spectroscopy and size exclusion chromatography (SEC). The dependence of unfolding on heating rate indicated that the thermal denaturation of the protein was at least partly under kinetic control. The data was interpreted in terms of a simple two-state kinetic model, N(Native) k --> A(Aggregated), where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation. Analysis of the data in terms of the above scheme suggested that under the experimental conditions used in this study, the rate-controlling step in the aggregation of rFVIII may be a unimolecular reaction involving conformational changes.

A single mutation induces amyloid aggregation in the alpha-spectrin SH3 domain: analysis of the early stages of fibril formation

The Src-homology region 3 domain of chicken alpha-spectrin (Spc-SH3) is a small two-state folding protein, which has never been described to form amyloid fibrils under any condition investigated so far. We show here that the mutation of asparagine 47 to alanine at the distal loop, which destabilises similarly the native and folding transition states of the domain, induces the formation of amyloid fibrils under mild acid conditions. Amyloid aggregation of the mutant is enhanced by the increase in temperature, protein concentration and NaCl concentration. The early stages of amyloid formation have been monitored as a function of time and temperature using a variety of biophysical methods. Differential scanning calorimetry experiments under conditions of amyloid formation have allowed the identification of different thermal transitions corresponding to conformational and aggregation processes as well as to the high-temperature disaggregation and unfolding of the amyloid fibrils. Aggregation is preceded by a rapid conformational change in the monomeric domain involving about 40% of the global unfolding enthalpy, considerable change in secondary structure, large loss of tertiary structure and exposure of hydrophobic patches to the solvent. The conformational change is followed by formation of a majority of oligomeric species with apparent hydrodynamic radius between 2.5 nm and 10nm, depending on temperature, together with the appearance and progressive growth of protofibrillar aggregates. After these early aggregation stages, long and curved fibrils of up to several micrometers start to develop by elongation of the protofibrils. The calorimetric data indicate that the specific enthalpy of fibril disaggregation and unfolding is relatively low, suggesting a low density of interactions within the fibril structure as compared to the native protein and a main entropy contribution to the stability of the amyloid fibrils.

Measurements of binding thermodynamics in drug discovery

Thermodynamics governs the process of biomolecular recognition. The steps of characterizing, understanding and exploiting binding thermodynamics have the potential to contribute to an improved rational drug design process that is more robust and reliable. It is only relatively recently that instrumentation capable of direct and full thermodynamic characterization has been improved, giving impetus to the application of thermodynamic measurements in drug discovery. This review highlights current instruments and methods that can be employed to measure binding thermodynamics and their use in studies of biomolecular recognition and drug discovery.

Evaluation of riboflavin binding protein domain interaction using differential scanning calorimetry

Riboflavin binding (or carrier) protein (RfBP) is a monomeric, two-domain protein, originally purified from hens' egg white. RfBP contains nine disulfide bridges; as a result, the protein forms a compact structure and undergoes reversible three-state thermal denaturation. This was demonstrated using a differential scanning calorimetry (DSC) method [Wasylewski M. (2000) J. Prot. Chem. 19(6), 523-528]. It has been shown that the RfBP complex with riboflavin denaturates in a three-state process which may be attributed to sequential unfolding of the RfBP domains. In case of apo RfBP, the ligand binding domain denaturates at a lower temperature than the C-terminal domain. Ligand binding greatly enhances the thermostability of the N-terminal domain, whereas the C-terminal domain thermostability is only slightly affected and, in case of the examined holo RfBPs, the denaturation peaks of both domains merge or cross over. The magnitude of the changes depends on ligand structure. A detailed study of protein concentration effects carried out in this work allowed to estimate not only the thermostability of both domains but also the strength of domain interactions. The DeltaCp, of denaturation was found for C-terminus and N-terminus of RfBP-riboflavin complex to amount to 2.5 and -1.9 kcal mol(-1), respectively. The calculated domain interaction free energy, DeltaGCN, was estimated to be approximately -1580 cal mol(-1) at 67.0 degrees C. This value indicates that the interdomain interaction is of medium strength.

Protein thermal aggregation involves distinct regions: sequential events in the heat-induced unfolding and aggregation of hemoglobin

Protein thermal aggregation plays a crucial role in protein science and engineering. Despite its biological importance, little is known about the mechanism and pathway(s) involved in the formation of aggregates. In this report, the sequential events occurring during thermal unfolding and aggregation process of hemoglobin were studied by two-dimensional infrared correlation spectroscopy. Analysis of the infrared spectra recorded at different temperatures suggested that hemoglobin denatured by a two-stage thermal transition. At the initial structural perturbation stage (30-44 degrees C), the fast red shift of the band from alpha-helix indicated that the native helical structures became more and more solvent-exposed as temperature increased. At the thermal unfolding stage (44-54 degrees C), the unfolding of solvent-exposed helical structures dominated the transition and was supposed to be responsible to the start of aggregation. At the thermal aggregation stage (54-70 degrees C), the transition was dominated by the formation of aggregates and the further unfolding of the buried structures. A close inspection of the sequential events occurring at different stages suggested that protein thermal aggregation involves distinct regions.

Physical stability of proteins in aqueous solution: mechanism and driving forces in nonnative protein aggregation

Irreversible protein aggregation is problematic in the biotechnology industry, where aggregation is encountered throughout the lifetime of a therapeutic protein, including during refolding, purification, sterilization, shipping, and storage processes. The purpose of the current review is to provide a fundamental understanding of the mechanisms by which proteins aggregate and by which varying solution conditions, such as temperature, pH, salt type, salt concentration, cosolutes, preservatives, and surfactants, affect this process.

Controlled release of a model protein lysozyme from phase sensitive smart polymer systems

The purpose of this study was to investigate the suitability of phase sensitive smart polymer-based protein formulations in order to deliver a model protein, lysozyme, in a conformationally stable and biologically active form at a controlled rate over extended period of time. Four different formulations, using D,L-poly(lactide) (D,L-PLA) and a solvent mixture of different ratios of benzyl benzoate (BB) and benzyl alcohol (BA), were prepared. Conformational stability and biological activity of lysozyme were studied by differential scanning calorimeter and enzyme activity assay, respectively. We found a significant (P < 0.05) increase in burst and rate of release of incorporated lysozyme from formulations containing greater proportion of BA. In order to increase the conformational stability and biological activity of lysozyme, we incorporated mannitol as stabilizer into formulations. Mannitol increased the conformational and biological activity of lysozyme in comparison to the control formulation prepared without mannitol. In conclusion, phase sensitive smart polymer-based delivery systems were able to deliver a model protein, lysozyme, in a conformationally stable and biologically active form at a controlled rate over extended period of time.

Streptokinase—a clinically useful thrombolytic agent

A failure of hemostasis and consequent formation of blood clots in the circulatory system can produce severe outcomes such as stroke and myocardial infraction. Pathological development of blood clots requires clinical intervention with fibrinolytic agents such as urokinase, tissue plasminogen activator and streptokinase. This review deals with streptokinase as a clinically important and cost-effective plasminogen activator. The aspects discussed include: the mode of action; the structure and structure-function relationships; the structural modifications for improving functionality; recombinant streptokinase; microbial production; and recovery of this protein from crude broths.

Aggregation of bovine insulin probed by DSC/PPC calorimetry and FTIR spectroscopy

Pressure perturbation calorimetry (PPC), differential scanning calorimetry (DSC), and time-resolved Fourier transform infrared spectroscopy (FTIR) have been employed to investigate aggregation of bovine insulin at pH 1.9. The aggregation process exhibits two distinguished phases. In the first phase, an intermediate molten globule-like conformational state is transiently formed, reflected by loose tertiary contacts and a robust H/D-exchange. This is followed by unfolding of the native secondary structure. The unfolding of insulin is fast, endothermic, partly reversible, and accompanied by a volume expansion of approximately 0.2%. The second phase consists of actual aggregation: an exothermic irreversible process revealing typical features of nucleation-controlled kinetics. The volumetric changes associated with the second phase are small. The concentration-dependence of DSC scans does not support a monomer intermediate model. While insulin aggregation under ambient pressure is fast and quantitative, pressure as low as 300 bar is sufficient to prevent the aggregation completely, as high-pressure FTIR spectroscopy revealed. This is explained in terms of the high pressure having an adverse effect on the thermal unfolding of insulin, and therefore preventing occurrence of the aggregation-prone intermediate. A comparison of the aggregation in H(2)O and D(2)O shows that the isotopic substitution has diverse effects on both the phases of aggregation. In heavy water, a more pronounced volume expansion accompanies the unfolding stage, while only the second phase shifts to higher temperature.

Thermal denaturation of spinach plastocyanin: effect of copper site oxidation state and molecular oxygen

The thermal denaturation of the cupredoxin plastocyanin (PC) from spinach has been studied with the aim of improving the understanding of factors involved in the conformational stability of antiparallel beta-sheet proteins. Studies using differential scanning calorimetry have been complemented with nuclear magnetic resonance spectroscopy, absorbance spectroscopy, dynamic light scattering, and mass spectrometry in elucidation of the effect of the copper-site oxidation state on the irreversible thermal denaturation process. Our results indicate that copper-catalyzed oxidation of the metal-ligating cysteine is the sole factor resulting in thermal irreversibility. However, this can be prevented in reduced protein by the removal of molecular oxygen. Application of a two-state equilibrium transition model to the folding process thus allowed the extraction of thermodynamic parameters for the reduced protein (Delta(trs)H = 494 kJ mol(-1), DeltaH(vH) = 343 kJ mol(-1), and T(m) = 71 degrees C). However, anaerobically denatured oxidized protein and all aerobically denatured species undergo covalent modification as a result of the copper-catalyzed oxidation of the metal-ligating cysteine residue resulting in the formation of both oxidized monomers and disulfide-linked dimers. On the basis of these results, a general mechanism for the irreversible thermal denaturation of cupredoxins is proposed. The results presented here also indicate that PC, as opposed to the previously characterized homologous protein azurin, unfolds via at least one significantly populated intermediate state (DeltaH(vH)/Delta(trs)H = 0.7) despite the almost identical native state topologies of these proteins. These findings will aid the characterization of the stability of PC and other cupredoxins and possibly of all cysteine-ligating metal-binding proteins.

Applications of calorimetric methods to drug discovery and the study of protein interactions

Recent studies report the application of isothermal titration calorimetry and differential scanning calorimetry to the study of protein-ligand interactions, allosteric cooperativity and aspects of protein folding. New methods of data analysis compare alternative methods for determining ligand binding enthalpy and analyze potential sources of error in the experimental measurement of other thermodynamic parameters. Several reports examine issues concerning drug design and the correlation of thermodynamic and X-ray structural data. New instruments allow volumetric effects in biochemical systems to be evaluated calorimetrically and to substantially expand the throughput of differential scanning calorimetry measurements in drug discovery and other high-throughput applications.