Generation of a novel fully human non-superagonistic anti-CD28 antibody with efficient and safe T-cell co-stimulation properties

Antibody-based therapeutics represent an important class of biopharmaceuticals in cancer immunotherapy. CD3 bispecific T-cell engagers activate cytotoxic T-cells and have shown remarkable clinical outcomes against several hematological malignancies. The absence of a costimulatory signal through CD28 typically leads to insufficient T-cell activation and early exhaustion. The combination of CD3 and CD28 targeting products offers an attractive strategy to boost T-cell activity. However, the development of CD28-targeting therapies ceased after TeGenero's Phase 1 trial in 2006 evaluating a superagonistic anti-CD28 antibody (TGN1412) resulted in severe life-threatening side effects. Here, we describe the generation of a novel fully human anti-CD28 antibody termed "E1P2" using phage display technology. E1P2 bound to human and mouse CD28 as shown by flow cytometry on primary human and mouse T-cells. Epitope mapping revealed a conformational binding epitope for E1P2 close to the apex of CD28, similar to its natural ligand and unlike the lateral epitope of TGN1412. E1P2, in contrast to TGN1412, showed no signs of in vitro superagonistic properties on human peripheral blood mononuclear cells (PBMCs) using different healthy donors. Importantly, an in vivo safety study in humanized NSG mice using E1P2, in direct comparison and contrast to TGN1412, did not cause cytokine release syndrome. In an in vitro activity assay using human PBMCs, the combination of E1P2 with CD3 bispecific antibodies enhanced tumor cell killing and T-cell proliferation. Collectively, these data demonstrate the therapeutic potential of E1P2 to improve the activity of T-cell receptor/CD3 activating constructs in targeted immunotherapeutic approaches against cancer or infectious diseases.

Common architecture of Tc toxins from human and insect pathogenic bacteria

Tc toxins use a syringe-like mechanism to penetrate the membrane and translocate toxic enzymes into the host cytosol. They are composed of three components: TcA, TcB, and TcC. Low-resolution structures of TcAs from different bacteria suggest a considerable difference in their architecture and possibly in their mechanism of action. Here, we present high-resolution structures of five TcAs from insect and human pathogens, which show a similar overall composition and domain organization. Essential structural features, including a trefoil protein knot, are present in all TcAs, suggesting a common mechanism of action. All TcAs form functional pores and can be combined with TcB-TcC subunits from other species to form active chimeric holotoxins. We identified a conserved ionic pair that stabilizes the shell, likely operating as a strong latch that only springs open after destabilization of other regions. Our results provide new insights into the architecture and mechanism of the Tc toxin family.

Clinical usefulness of therapeutic concentration monitoring for imatinib dosage individualization: results from a randomized controlled trial

PURPOSE

This study assessed whether a cycle of "routine" therapeutic drug monitoring (TDM) for imatinib dosage individualization, targeting an imatinib trough plasma concentration (C min) of 1,000 ng/ml (tolerance: 750-1,500 ng/ml), could improve clinical outcomes in chronic myelogenous leukemia (CML) patients, compared with TDM use only in case of problems ("rescue" TDM).

METHODS

Imatinib concentration monitoring evaluation was a multicenter randomized controlled trial including adult patients in chronic or accelerated phase CML receiving imatinib since less than 5 years. Patients were allocated 1:1 to "routine TDM" or "rescue TDM." The primary endpoint was a combined outcome (failure- and toxicity-free survival with continuation on imatinib) over 1-year follow-up, analyzed in intention-to-treat (ISRCTN31181395).

RESULTS

Among 56 patients (55 evaluable), 14/27 (52 %) receiving "routine TDM" remained event-free versus 16/28 (57 %) "rescue TDM" controls (P = 0.69). In the "routine TDM" arm, dosage recommendations were correctly adopted in 14 patients (median C min: 895 ng/ml), who had fewer unfavorable events (28 %) than the 13 not receiving the advised dosage (77 %; P = 0.03; median C min: 648 ng/ml).

CONCLUSIONS

This first target concentration intervention trial could not formally demonstrate a benefit of "routine TDM" because of small patient number and surprisingly limited prescriber's adherence to dosage recommendations. Favorable outcomes were, however, found in patients actually elected for target dosing. This study thus shows first prospective indication for TDM being a useful tool to guide drug dosage and shift decisions. The study design and analysis provide an interesting paradigm for future randomized TDM trials on targeted anticancer agents.

Photokinetische Untersuchungen an den photochromen Systemen der Dihydroindolizine

The dependence of partial photochemical quantum yields on temperature and light intensity was examined with two dihydroindolizines. Some nonlinear optimization procedures and least squares methods are used to solve the system of differential equations. The distinct influence of the competitive thermal reaction can be demonstrated for both photochromic systems by determination of thermodynamic and kinetic parameters.

The transport of potassium through lipid bilayer membranes by the neutral carriers valinomycin and monactin : Experimental studies to a previously proposed model

Stationary conductance experiments on neutral and negatively charged bilayer membranes in the presence of valinomycin or monactin agree with a recently proposed carrier transport model, which is common to both carrier types. This model assumes an interface reaction between a cation from the aqueous solution and a carrier molecule from the membrane phase to establish charge transport across the interface. The transport across the membrane interior is described by some kind of "Eyring model". The discussion of the current-voltage characteristic, the dependence of membrane conductance on the carrier and K(+) concentrations, and the comparison with appropriate experiments allow correlation of the different rate constants of the transport model. The results show that the rate constants partly depend on the surface charge of the membranes. This dependency can be described by introducing the Gouy-Chapman theory for charged surfaces into the transport model.It was found that the carrier molecules could be added either to the aqueous phase or to the membrane-forming solution. The quantitative treatment of this phenomenon gives an evaluation of the partition coefficient of the carrier molecules between the membrane bulk phase and water.

[Traumatic abruption of the placenta with disseminated intravascular coagulation]

Trauma in pregnancy is infrequent and a systematic primary strategy constitutes a real challenge for the interdisciplinary team. With a high fetal mortality rate and a substantial maternal mortality rate traumatic placental abruption is a severe emergency which every anesthetist should be aware of. After hemodynamic stabilization of the mother and control of the viability of the fetus the therapy of traumatic placental abruption consists mostly of an immediate caesarean section. Coagulopathy by depletion of coagulation factors as well as disseminated intravascular coagulation (DIC) have to be expected and consequently a massive blood loss must be anticipated. Thrombelastography provides assistance for fast differential diagnosis and goal-directed treatment of the disturbed sections of the coagulation cascade.

[Neuroradiological focus on stroke imaging]

Stroke is heterogenous in its symptoms, which are also caused by various pathologies. Clinically the causing mechanism (bleeding or ischemia) of a new onset of neurological deficits can not reliably be distinguished. However, ischemia is four times more frequent than a bleeding causing neurological symptoms. Modern imaging technologies (computed assisted tomography or magnetic resonace imaging) and interventional techniques are a mainstay in diagnostics and management of acute onset of neurological symptoms. They can reliably distinguish between bleeding and stroke, especially taking newest technologies, such as perfusion studies and angiographies, into account. Neuroradiology with its interventional options has nowadays furthermore become an important tool in strokes and offers a local maneuver to retrieve the clotting pathology and even opens the therapeutic window for a delayed start of the therapy since symptom's onset beyong the conventional 4.5 hours window. Also risks of a therapy and which therapy option should be used can immediately be assessed.

The voltage-dependent step of the chloride transporter of Valonia utricularis encounters a Nernst-Planck and not an Eyring type of potential energy barrier

Voltage-clamp experiments were performed on cells of the giant marine alga Valonia utricularis to study the voltage dependence of the previously postulated chloride transporter (Wang, J., G. Wehner, R. Benz, and U. Zimmermann. 1991. Biophys. J. 59:235-248). Only one exponential current relaxation (apart from the capacitive spike) could be resolved up to a clamp voltage of approximately 120 mV within the time resolution of our experimental instrumentation (100 mus). This means that the rate constants of the heterogeneous complexation, k(R) (association) and k(D) (dissociation), were too fast to be resolved. Therefore, the "Läuger" model for carrier-mediated ion transport with equilibrium heterogeneous surface reaction was used to fit the experimental results. The voltage dependence of the initial membrane conductance was used for the evaluation of the voltage dependence of the translocation rate constant of the complexed carriers, k(AS). The initial conductance was found to be independent on the clamp voltage, which means that the translocation rate constant k(AS) is a linear function of the applied voltage and that the voltage dependence of the translocation of charged carriers through the plasmalemma could be explained by a square-type Nernst-Planck barrier. The movement of the complexed form of the carrier through the membrane may be explained by a diffusion process rather than by simple first-order kinetic jump across an Eyring-type potential well. The current relaxation after a voltage clamp was studied as a function of the external chloride concentration. The results allowed an estimation of the stability constant, K, of the heterogeneous complexation reaction and a calculation of the translocation rate constants of the free and the complexed carriers, k(s) and k(AS), respectively.

Harmonic system analysis of the algae Valonia utricularis: contribution of an electrogenic transport system to gain and phase-shift of the transfer function

Cell membrane properties of the giant marine alga Valonia utricularis were measured in the frequency domain between 1 Hz and 10 MHz by harmonic system analysis. Harmonic analysis was performed by imposing a sinusoidal electrical voltage on the cell interior via an internal microelectrode. Gain and phase-shift of the resulting sinusoidal membrane voltage were measured over the whole frequency range with an internal voltage microelectrode. Bode plots of gain and phase-shift allowed the determination of the electrical parameters of the equivalent electronic circuits of the cell membrane of V. utricularis, which showed dynamic and passive properties dependent on the pH of the external aqueous solution. The dynamic components of the membrane impedance were caused by an electrogenic transport system for chloride described previously (Wang, J., G. Wehner, R. Benz, and U. Zimmermann. 1991. Biophys. J. 59:235-248). The kinetic and equilibrium parameters of the transport system could be evaluated from the fit of Bode plots of gain and phase-shift. The frequency domain technique revealed complete agreement of transport parameters with previously published results. The data demonstrate that an electrogenic transport system can be driven by an oscillating electric field.

Characterization of channel-forming activity in muscle biopsy from a porin-deficient human patient

A bioptic specimen from the muscles of a patient suffering from severe myopathy was inspected for the presence of human porin 31HL. Western blotting suggested that the specimen was free of the most abundant eukaryotic porin 31HL (HVDAC1). The specimen was treated with detergent and the soluble protein fraction was passed through a dry hydroxyapatite column. The passthrough of this column was inspected for channel formation in artificial lipid-bilayer membranes. The channel observed under these conditions had a single-channel conductance of about 2.5 nS in 1 M KCl, was cation selective, and was found to be virtually voltage independent. Experiments with a control specimen from a healthy human being, without any indication for muscle myopathy, revealed the presence of the voltage-dependent porin 31HL in the sample. It is discussed whether the patient's bioptic specimen contained another human porin, which has not been studied to date in its natural environment.

Functional characterization of the conserved "GLK" motif in mitochondrial porin from Neurospora crassa

Mitochondrial porin facilitates the diffusion of small hydrophilic molecules across the mitochondrial outer membrane. Despite low sequence similarity among porins from different species, a "glycine-leucine-lysine" (GLK) motif is conserved in mitochondrial and Neisseria porins. To investigate the possible roles of these conserved residues, including their hypothesized participation in ATP binding by the protein, we replaced the lysine residue of the GLK motif of Neurospora crassa porin with glutamic acid through site-directed mutagenesis of the corresponding gene. Although the pores formed by this protein have size and gating characteristics similar to those of the wild-type protein, the channels formed by GLEporin are less anion selective than the wild-type pores. The GLEporin retains the ability to be cross linked to [alpha-(32)P]ATP, indicating that the GLK sequence is not essential for ATP binding. Furthermore, the pores formed by both GLEporin and the wild-type protein become more cation selective in the presence of ATP. Taken together, these results support structural models that place the GLK motif in a part of the ion-selective beta-barrel that is not directly involved in ATP binding.

Structure-function correlation of outer membrane protein porin from Paracoccus denitrificans

Porins from outer membrane of Gram-negative bacteria have a highly stable structure. Our previous studies on porin from Paracoccus denitrificans showed that the outer membrane protein porin is extremely stable toward heat, pH, and chemical denaturants. The major question we have addressed in this paper is whether the high stability of porin is a consequence of the beta-barrel structure and whether it is required for its function. To explain this we have analyzed two cases: first, we used porin wild-type and mutants and compared their structure and function; second, we compared the activity of porin preheated to different temperatures. Structural changes were monitored by infrared spectroscopy. We observed that the structural stability of porin is not equivalent to functional activity as minor alteration in the structure can result in drastic differences in the activity of porins.

Solute traffic across mammalian peroxisomal membrane – single channel conductance monitoring reveals pore-forming activities in peroxisomes

Mouse liver peroxisomes were isolated by centrifugation in a self-generated Percoll gradient followed by an Optiprep density gradient centrifugation. Peroxisomes contributed 90-96% of the total protein content in the fraction, as confirmed by marker enzyme assays, protein pattern in SDS-PAGE, immunoblotting, and electron microscopy. Solubilized peroxisomal membrane proteins were reconstituted into a planar lipid bilayer. A single-channel conductance monitoring of the reconstituted lipid bilayer revealed the presence of two pore-forming components with a conductance in 1 M KCl of 1.3 nS and 2.5 nS. Control experiments with fractions enriched in mitochondria, lysosomes, and fragments of endoplasmic reticulum showed that the peroxisomal channel-forming activities were not due to admixture of isolated peroxisomes with other cellular organelles. The peroxisomal channels were well preserved in membrane preparations but became unstable after solubilization from the membranes by detergent.

Nanopores: maltoporin channel as a sensor for maltodextrin and lambda-phage

Background

To harvest nutrition from the outside bacteria e.g. E. coli developed in the outer cell wall a number of sophisticated channels called porins. One of them, maltoporin, is a passive specific channel for the maltodextrin uptake. This channel was also named LamB as the bacterial virus phage Lambda mis-uses this channel to recognise the bacteria. The first step is a reversible binding followed after a lag phase by DNA injection. To date little is known about the binding capacity and less on the DNA injection mechanism. To elucidate the mechanism and to show the sensitivity of our method we reconstituted maltoporin in planar lipid membranes. Application of an external transmembrane electric field causes an ion current across the channel. Maltoporin channel diameter is around a few Angstroem. At this size the ion current is extremely sensitive to any modification of the channels surface. Protein conformational changes, substrate binding etc will cause fluctuations reflecting the molecular interactions with the channel wall. The recent improvement in ion current fluctuation analysis allows now studying the interaction of solutes with the channel on a single molecular level.

Results

We could demonstrate the asymmetry of the bacterial phage Lambda binding to its natural receptor maltoporin.

Conclusion

We suggest that this type of measurement can be used as a new type of biosensors.

[Low HDL-cholesterol, high triglycerides--well known but often ignored]

A reduced HDL-Cholersterol and increased triglyzerides are an often seen laboratory abnormality. They are known risk factors for arteriosclerosis. However the small influence of a pharamcologic treatment on the two reduced the interest in them. We therefore want to show the relation of the triglyzerides with the HDL-Cholesterol and the nonpharmacologic treatment of these two factors. Some clinical examples are illustrating the topic.

[Elevated lipid levels during pregnancy--what to do?]

Based on a clinical case we discuss the physiological changes in the lipid metabolism during pregnancy. The changes are characterised by a marked elevation of the total plasma cholesterol and the triglyceride levels. Usually there is no need for a specific therapy.

Electromagnetic field-based image-guided spine surgery part one: results of a cadaveric study evaluating lumbar pedicle screw placement

STUDY DESIGN

Human cadaveric.

OBJECTIVES

Compare the accuracy of electromagnetic field (EMF)-based image-guided lumbar pedicle screw insertion to conventional techniques using anatomic landmarks, and fluoroscopy.

BACKGROUND

Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF tracking-based image-guidance was developed in the hopes of eliminating line-of-sight restrictions seen with other systems.

MATERIALS AND METHODS

Sixteen fresh-frozen human cadavers were randomly allocated into three groups. Pedicle screws were inserted from L1 to L5 using only anatomic landmarks in group 1, fluoroscopy in group 2, and image-guidance in group 3. Insertion and total fluoroscopic time were recorded. Anatomic dissections were performed to assess screw placement.

RESULTS

Accuracy was 83%, 78%, and 95% for groups 1, 2, and 3, respectively. However, image-guided pedicle screw placement resulted in a 5% critical perforation rate whereas anatomic and fluoroscopic placement resulted in a 15% and 22% critical perforation rate, respectively. The average degree of perforation was 1.5 mm with image guidance, and 3.8 mm with fluoroscopic guidance (P < 0.05). Fluoroscopy time and insertion time per screw were not improved using image guidance.

CONCLUSIONS

Our study has shown that when EMF tracking was used for image-guided lumbar pedicle screw placement, accuracy was improved and the incidence and degree of cortical perforations that may place neurovascular structures at risk was also reduced. Current system requirements for set-up and image acquisition, however, do add time to the procedure, and when factored in, do not yet result in a decrease in the use of fluoroscopy or screw insertion time.

[It's so good that nobody knows my name]

Anhand eines Falles am Zuger Kantonsspital wird die Biologie und medizinische Bedeutung der gemeinen Stechfliege (Stomoxys calcitrans) oder im Volkmund «Wadenbeisser» aufgearbeitet. Sie ernährt sich von Blut und sticht auch Menschen, was die Frage von übertragbaren Krankheiten aufwirft. Es finden sich in der Literatur nur einzelne Fallberichte, die eine Übertragung von Milzbrand, Borreliose, Tularämie und Erysipeloid durch die Stechfliege beschreiben. Tropische Krankheitserreger wie Trypanosmen, Plasmodien oder Dengueviren werden nur durch bei uns nicht heimische Vektoren übertragen.

Site-directed mutagenesis within the central constriction site of ScrY (sucroseporin): effect on ion transport and comparison of maltooligosaccharide binding to LamB of Escherichia coli

The 3-D structures of the maltooligosaccharide-specific LamB-channel of Escherichia coli (also called maltoporin) and sucrose-specific ScrY (sucroseporin) are known from X-ray crystallography. The central constriction of the channels formed by the external loop 3 is controlled by a number of different amino acids. The most prominent one of these, N192, D201 and F204, were replaced by site-directed mutagenesis into those of LamB, which, according to the 3-D model of both channels are localized at similar places. The ScrY single mutants ScrYN192R, ScrYD201Y and ScrYF204D and the ScrY triple mutant ScrY3113 (N192R + D201Y + F204D) were created together with the triple mutant ScrY3213, which lacks also amino acids 1 to 61 from the N-terminal end. The mutant proteins were purified to homogeneity and were reconstituted into lipid bilayer membranes. In these experiments, the single-channel conductance of the mutants in different salt solutions and the stability constants for binding of different maltooligosaccharides to the mutant channels was measured using titration experiments with carbohydrates. The carbohydrate-induced block of the channel function could also be used for the study of current noise through the different mutant ScrY-channels. The analysis of the power density spectra allowed the evaluation of the on- and off-rate constants (k1 and k-1) of carbohydrate-binding to the binding site inside the channels. The results suggest that both on- and off-rate constants were affected by the mutations. Most of them showed a substantial effect on carbohydrate binding kinetics. Nevertheless, single-channel conductance and carbohydrate binding of ScrY3113 mutant were still different from that of LamB, suggesting that not only the amino acids of the central constriction but also the general architecture of both channels have a substantial influence on channel properties.

Channel formation by salmon and human calcitonin in black lipid membranes

In this study we investigated the interaction of salmon and human calcitonin (Ct) with artificial lipid bilayer membranes. Both peptides were able to form either transient or permanent channels in the model membranes. The channels formed by salmon Ct at concentration (125 nM) had, on average, a single-channel conductance of 0.58 +/- 0.04 nS in 1M KCl (+10 mV), which is voltage-dependent at lower voltages. Human Ct forms at the same concentration channels with a much lower probability, and high voltages of up to +150 mV were needed to initiate channel formation. The estimated single-channel conductance formed under these conditions was approximately 0.0119 +/- 0.0003 nS in 1 M KCl. Both salmon and human Ct channels were found to be permeable to calcium ions. The possibility is discussed that the superior therapeutic effect of salmon Ct as a tool to treat bone disorders, including Paget disease, osteoporosis, and hypercalcemia of malignancy, rather than human Ct is related to the lack of the fibrillating property of salmon Ct. Preliminary data indicate that also eel and porcine Ct and carbocalcitonin form channels in model membranes.

Identification of a cell wall channel of Streptomyces griseus: the channel contains a binding site for streptomycin

Cells of the Gram-positive actinomycete Streptomyces griseus were disrupted and the cell envelope was subjected to sucrose step-gradient centrifugation. The different fractions were analysed for NADH-oxidase activity and the formation of ion-permeable channels in lipid bilayers. Highest channel-forming activity and highest NADH-oxidase activity were found in different fractions. The cell wall fraction contained an ion-permeable channel with a single-channel conductance of 850 pS in 1 M KCl. The channel-forming protein, with an apparent molecular mass of 28 kDa, was purified to homogeneity using fast protein liquid chromatography after the extraction of whole cells with detergent. Single-channel experiments suggest that the cell wall channel is wide and water-filled. Titration experiments with streptomycin produced by S. griseus suggested that the cell wall channel binds this antibiotic with a half saturation constant of about 6 mM in 1 M KCl. The binding of streptomycin was found to be ionic strength dependent and the half saturation constant decreased to 60 microM at 0.1 M KCl. The results indicate that the 28 kDa protein represents the hydrophilic pathway through the cell wall of the Gram-positive bacterium S. griseus.

Phloretin-induced changes of lipophilic ion transport across the plasma membrane of mammalian cells

The adsorption of the hydrophobic anion [W(CO)(5)CN](-) to human lymphoid Jurkat cells gave rise to an additional anti-field peak in the rotational spectra of single cells, indicating that the cell membrane displayed a strong dielectric dispersion in the kilohertz to megahertz frequency range. The surface concentration of the adsorbed anion and its translocation rate constant between the two membrane boundaries could be evaluated from the rotation spectra of cells by applying the previously proposed mobile charge model. Similar single-cell electrorotation experiments were performed to examine the effect of phloretin, a dipolar molecule known to influence the dipole potential of membranes, on the transport of [W(CO)(5)CN](-) across the plasma membrane of mammalian cells. The adsorption of [W(CO)(5)CN](-) was significantly reduced by phloretin, which is in reasonable agreement with the known phloretin-induced effects on artificial and biological membranes. The IC(50) for the effect of phloretin on the transport parameters of the lipophilic ion was approximately 10 microM. The results of this study are consistent with the assumption that the binding of phloretin reduces the intrinsic dipole potential of the plasma membrane. The experimental approach developed here allows the quantification of intrinsic dipole potential changes within the plasma membrane of living cells.

Study of the properties of a channel-forming protein of the cell wall of the gram-positive bacterium Mycobacterium phlei

The gram-positive bacterium Mycobacterium phlei was treated with detergents. Reconstitution experiments using lipid bilayers suggested that the detergent extracts contain a channel forming protein. The protein was purified to homogeneity by preparative SDS-PAGE and identified as a protein with an apparent molecular mass of about 135 kDa. The channel-forming unit dissociated into subunits with a molecular mass of about 22 kDa when it was boiled in 80% dimethylsulfoxid (DMSO). The channel has on average a single channel conductance of 4.5 nS in 1 m KCl and is highly voltage-dependent in an asymmetric fashion when the protein is added to only one side of the membrane. Zero-current membrane potential measurements with different salts implied that the channel is highly cation-selective because of negative point charges in or near the channel mouth. Analysis of the single-channel conductance as a function of the hydrated cation radii using the Renkin correction factor and the effect of the negative point charges on the single-channel conductance suggest that the diameter of the cell wall channel is about 1.8 to 2.0 nm. The channel properties were compared with those of other members of the mycolata and suggest that these channels share common features. Southern blots demonstrated that the chromosome of M. phlei and other mycolata tested contain homologous sequences to mspA (gene of the cell wall porin of Mycobacterium smegmatis).

Risk factors for hypertension in chronic hemodialysis patients: baseline data from the HEMO study

A cross-sectional analysis was performed to determine risk factors associated with hypertension in 1,238 chronic hemodialysis patients upon enrollment into the HEMO Study. The mean pre- and post-dialysis systolic blood pressure were 152.4 +/- 25.0 (mean +/- SD) and 137.8 +/- 24.6 mm Hg, respectively. The mean pre- and post-dialysis diastolic blood pressures were 82.1 +/- 14.8 and 74.7 +/- 13.8 mm Hg, respectively. Less than 30% of the study cohort had blood pressures that were normotensive by JNC VI guidelines. Risk factors associated with higher pre- and post-dialysis systolic blood pressures included the presence of diabetes mellitus, older age, increased number of prescribed antihypertensive medications, lower hematocrit, and absence of arrhythmias. Variables associated with higher pre- and post-dialysis diastolic blood pressures included younger age, increased number of prescribed anti-hypertensive medications and absence of arrhythmias. There was also a nonlinear relationship between blood pressure and prescribed total ultrafiltration volume. A total ultrafiltration volume of >2.5 kg was associated with an elevation in pre-dialysis systolic and diastolic blood pressures. A total ultrafiltration volume of < or =2.5 kg was associated with an elevation in post-dialysis systolic and diastolic blood pressures. These data on ultrafiltration volume suggest that higher pre-dialysis blood pressures may be associated with excessive interdialytic weight gains due to patient noncompliance with fluid restriction and that higher post-dialysis blood pressures may be associated with a prescribed dry weight that is higher than the patient's true dry weight. Better management of these parameters may improve the prevalence and severity of hypertension in this population.

Clostridium perfringens epsilon toxin induces a rapid change of cell membrane permeability to ions and forms channels in artificial lipid bilayers

Epsilon toxin is a potent toxin produced by Clostridium perfringens types B and D, which are responsible for a rapidly fatal enterotoxemia in animals. One of the main properties of epsilon toxin is the production of edema. We have previously found that epsilon toxin causes a rapid swelling of Madin-Darby canine kidney cells and that the toxin does not enter the cytosol and remains associated with the cell membrane by forming a large complex (Petit, L., Gibert, M., Gillet, D., Laurent-Winter, C., Boquet, P., and Popoff, M. R. (1997) J. Bacteriol. 179, 6480-6487). Here, we report that epsilon toxin induced in Madin-Darby canine kidney cells a rapid decrease of intracellular K(+), and an increase of Cl(-) and Na(+), whereas the increase of Ca(2+) occurred later. The entry of propidium iodide that was correlated with the loss of cell viability monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test indicates that epsilon toxin formed large pores. In artificial lipid bilayers, epsilon toxin caused current steps with a single-channel conductance of 60 pS in 100 mm KCl, which represented general diffusion pores. The channels were slightly selective for anions, but cations could also penetrate. Epsilon toxin formed wide and water-filled channels permeable to hydrophilic solutes up to a molecular mass of at least 1 kDa, which probably represents the basic mechanism of toxin action on target cells.

Low pH-induced formation of ion channels by clostridium difficile toxin B in target cells

Clostridium difficile toxin B (269 kDa), which is one of the causative agents of antibiotic-associated diarrhea and pseudomembranous colitis, inactivates Rho GTPases by glucosylation. Here we studied the uptake and membrane interaction of the toxin with eukaryotic target cells. Bafilomycin A1, which prevents acidification of endosomal compartments, blocked the cellular uptake of toxin B in Chinese hamster ovary cells cells. Extracellular acidification (pH </= 5.2) induced uptake of toxin B into the cytosol even in the presence of bafilomycin A1. Toxin B increased (86)Rb(+) release when preloaded Chinese hamster ovary cells were exposed to low pH (pH </= 5.6) for 5 min. Release of (86)Rb(+) depended on the concentration of toxin B and on the pH of the extracellular medium. An antibody directed against the holotoxin prevented channel formation, whereas an antibody against the N-terminal enzyme domain was without effect. The N-terminally truncated toxin B fragment consisting of amino acids 547-2366 increased (86)Rb(+) efflux when cells were exposed to low pH. Toxin B also induced pH-dependent channel formation in artificial lipid bilayer membranes. Clostridium sordellii lethal toxin, another member of the family of large clostridial cytotoxins, also induced increased (86)Rb(+) release at low pH. The results suggest that large clostridial cytotoxins including C. difficile toxin B and C. sordellii lethal toxin undergo structural changes at low pH of endosomes that are accompanied by membrane insertion and channel formation.

Interaction of phloretin with membranes: on the mode of action of phloretin at the water-lipid interface

The interaction of phloretin with single lipid bilayers on a spherical support and with multilamellar vesicles was studied by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The results indicated that phloretin interacts with the lipid layer and changes its structural parameters. In DSC experiments, phloretin in its neutral form strongly decreased the lipid phase transition temperature and slightly reduced the cooperativity of the phase transition within the lipid layer. In NMR measurements, phloretin led to an increase of the transverse relaxation time constant but had no effect on the spin-lattice relaxation time constant. The overall dipole moment of phloretin was experimentally determined and was found to be roughly 40% lower than has been published previously. This result suggested that the size of the dipole moment of phloretin does not provide such a high contribution to the effect of phloretin on the dipole potential of monolayers and bilayers as has been published previously. To understand the discrepancy between phloretin adsorption and dipole potential change, we performed computational conformational analysis of phloretin in the gas phase. The results showed that a wide distribution of the dipole moments of phloretin conformers exists, which mainly depends on the orientation of the OH moieties. The adsorption of phloretin as determined from its binding to solid supported bilayers differed from the one determined from dipole potential measurements on black lipid membranes. The difference between the phloretin dissociation constants of both types of experiments suggested a change of its dipole moment normal to the membrane surface in a concentration-dependent manner, which was in agreement with the results of the computational conformational analysis.

LcrV is a channel size-determining component of the Yop effector translocon of Yersinia

Delivery of Yop effector proteins by pathogenic Yersinia across the eukaryotic cell membrane requires LcrV, YopB and YopD. These proteins were also required for channel formation in infected erythrocytes and, using different osmolytes, the contact-dependent haemolysis assay was used to study channel size. Channels associated with LcrV were around 3 nm, whereas the homologous PcrV protein of Pseudomonas aeruginosa induced channels of around 2 nm in diameter. In lipid bilayer membranes, purified LcrV and PcrV induced a stepwise conductance increase of 3 nS and 1 nS, respectively, in 1 M KCl. The regions important for channel size were localized to amino acids 127-195 of LcrV and to amino acids 106-173 of PcrV. The size of the channel correlated with the ability to translocate Yop effectors into host cells. We suggest that LcrV is a size-determining structural component of the Yop translocon.

Identification of the outer membrane porin of Thermus thermophilus HB8: the channel-forming complex has an unusually high molecular mass and an extremely large single-channel conductance

The outer membrane of the thermophilic bacterium Thermus thermophilus was isolated using sucrose step gradient centrifugation. Its detergent extracts contained an ion-permeable channel with an extremely high single-channel conductance of 20 nS in 1 M KCl. The channel protein was purified by preparative sodium dodecyl sulfate (SDS)-polyacylamide gel electrophoresis. It has a high molecular mass of 185 kDa, and its channel-forming ability resists boiling in SDS for 10 min.

The low-molecular-mass subunit of the cell wall channel of the Gram-positive Corynebacterium glutamicum. Immunological localization, cloning and sequencing of its gene porA

The 5-kDa protein PorA of the Gram-positive bacterium Corynebacterium glutamicum is the subunit of the cell wall channel. Antibodies raised against PorA specifically detected the protein on the cell surface. PorA was sequenced using Edman degradation and a gas phase sequencer. The primary sequence was used to create degenerate oligonucleotide primers. The gene of the channel-forming protein and its flanking regions were obtained by PCR followed by inverse PCR. The gene porA comprises 138 bp and encodes a 45-amino-acid-long acidic polypeptide with an excess of four negatively charged amino acids in agreement with the high cation selectivity of the PorA cell wall channel. PorA does not contain an N-terminal extension. A ribosomal-binding site was recognized 6 bp before the start codon ATG of porA. It codes for the smallest subunit of a membrane channel known so far and for the first cell wall channel protein of a corynebacterium. Southern blots demonstrated that only the chromosomes of corynebacteria contain homologous sequences to porA; no hybridization could be detected with DNA from other mycolata.

Discovery of a novel channel-forming protein in the cell wall of the non-pathogenic Nocardia corynebacteroides

Detergent extracts of whole cells of the Gram-positive, non-pathogenic, strictly aerobic bacterium Nocardia corynebacteroides contain channel-forming activity. The protein responsible for channel formation was identified using lipid bilayer experiments. It was purified to homogeneity and had an apparent molecular mass of about 134 kDa on SDS-PAGE when it was solubilized at 40 degrees C. When the 134 kDa protein was heated to 100 degrees C for 10 min in sample buffer, it dissociated into subunits with a molecular mass of about 23 kDa and focused at pI of 4.5 during isoelectric focusing. The pure 134 kDa protein was able to increase the specific conductance of artificial lipid bilayer membranes from phosphatidylcholine-phosphatidylserine mixtures by the formation of ion-permeable channels. The channels had an average single-channel conductance of 5.5 nS in 1 M KCl and were found to be cation-selective. Asymmetric addition of the 134 kDa protein to lipid bilayer membranes resulted in an asymmetric voltage-dependence. The analysis of the single-channel conductance as a function of cation radii using the Renkin correction factor and the effect of negative charges on channel conductance suggested that the diameter of the cell wall porin is about 1.0 nm. The channel characteristics of the cell wall channel of N. corynebacteroides were compared with those of other members of the mycolata. They share common features because they are composed of small molecular mass subunits and form large and water-filled channels.

The C terminus of component C2II of Clostridium botulinum C2 toxin is essential for receptor binding

The binary Clostridium botulinum C2 toxin consists of two separate proteins, the binding component C2II (80.5 kDa) and the actin-ADP-ribosylating enzyme component C2I (49.4 kDa). For its cytotoxic action, C2II binds to a cell membrane receptor and induces cell entry of C2I via receptor-mediated endocytosis. Here we studied the structure-function relationship of C2II by constructing truncated C2II proteins and producing polyclonal antisera against selective regions of C2II. An antibody raised against the C terminus (amino acids 592 to 721) of C2II inhibited binding of C2II to cells. The antibody prevented pore formation by C2II oligomers in artificial membranes but did not influence the properties of existing channels. To further define the region responsible for receptor binding, we constructed proteins with deletions in C2II; specifically, they lacked amino acid residues 592 to 721 and the 7 C-terminal amino acid residues. The truncated proteins still formed sodium dodecyl sulfate-stable oligomers but were unable to bind to cells. Our data indicate that the C terminus of C2II mediates binding of the protein to cells and that the 7 C-terminal amino acids are structurally important for receptor binding.

Cellular uptake of Clostridium botulinum C2 toxin requires oligomerization and acidification

The actin-ADP-ribosylating binary Clostridium botulinum C2 toxin consists of two individual proteins, the binding/translocation component C2II and the enzyme component C2I. To elicit its cytotoxic action, C2II binds to a receptor on the cell surface and mediates cell entry of C2I via receptor-mediated endocytosis. Here we report that binding of C2II to the surface of target cells requires cleavage of C2II by trypsin. Trypsin cleavage causes oligomerization of the activated C2II (C2IIa) to give SDS-stable heptameric structures, which exhibit a characteristic annular or horseshoe shape and form channels in lipid bilayer membranes. Cytosolic delivery of the enzyme component C2I is blocked by bafilomycin but not by brefeldin A or nocodazole, indicating uptake from an endosomal compartment and requirement of endosomal acidification for cell entry. In the presence of C2IIa and C2I, short term acidification of the extracellular medium (pH 5.4) allows C2I to enter the cytosol directly. Our data indicate that entry of C2 toxin into cells involves (i) activation of C2II by trypsin-cleavage, (ii) oligomerization of cleaved C2IIa to heptamers, (iii) binding of the C2IIa oligomers to the carbohydrate receptor on the cell surface and assembly with C2I, (iv) receptor-mediated endocytosis of both C2 components into endosomes, and finally (v) translocation and release of C2I into the cytosol after acidification of the endosomal compartment.

Functional reconstitution of ICln in lipid bilayers

Reconstitution of purified ICln in lipid bilayer leads to functional ion channels showing varying rectification. The reconstituted single channels have a conductance of approximately equal to 3 pS and their open probability is sensitive to nucleoside analogues. Mutation of a putative nucleotide binding site identified at the predicted extracellular mouth of the ICln channel protein leads to the reduction of the nucleoside-analogue sensitivity. Reconstituted ICln channels can be permeated both by cations and anions. The relative permeability of cations over anions depends on the presence of calcium. In the presence of calcium reconstituted ICln channels are more permeable to bromide than chloride, and more permeable to potassium than sodium. Similarly in NIH3T3 fibroblasts, the relative permeability of cations over anions of swelling-dependent chloride channels depends on extracellular calcium. Site-directed mutagenesis revealed the calcium-binding site responsible for the shift of the selectivity from cations towards anions of reconstituted ICln channels. Additional indirect structural information has been obtained by mutating a histidine in the predicted pore region of ICln. This histidine seems to have access to the ion-conducting tunnel of the pore. Our experiments show that ICln can act as an ionic channel, which does not exclude additional functions of the protein in regulatory mechanisms of the cell. Since knocking down the ICln protein in fibroblasts and epithelial cells leads to an impaired regulatory volume decrease (RVD) after cytoplasmic swelling and reconstituted ICln channels show several biophysical features of ion channels activated after swelling, ICln is a molecular candidate for these channels.

Biochemical identification and biophysical characterization of a channel-forming protein from Rhodococcus erythropolis

Organic solvent extracts of whole cells of the gram-positive bacterium Rhodococcus erythropolis contain a channel-forming protein. It was identified by lipid bilayer experiments and purified to homogeneity by preparative sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). The pure protein had a rather low molecular mass of about 8.4 kDa, as judged by SDS-PAGE. SDS-resistant oligomers with a molecular mass of 67 kDa were also observed, suggesting that the channel is formed by a protein oligomer. The monomer was subjected to partial protein sequencing, and 45 amino acids were resolved. According to the partial sequence, the sequence has no significant homology to known protein sequences. To check whether the channel was indeed localized in the cell wall, the cell wall fraction was separated from the cytoplasmic membrane by sucrose step gradient centrifugation. The highest channel-forming activity was found in the cell wall fraction. The purified protein formed large ion-permeable channels in lipid bilayer membranes with a single-channel conductance of 6.0 nS in 1 M KCl. Zero-current membrane potential measurements with different salts suggested that the channel of R. erythropolis was highly cation selective because of negative charges localized at the channel mouth. The correction of single-channel conductance data for negatively charged point charges and the Renkin correction factor suggested that the diameter of the cell wall channel is about 2.0 nm. The channel-forming properties of the cell wall channel of R. erythropolis were compared with those of other members of the mycolata. These channels have common features because they form large, water-filled channels that contain net point charges.

In vivo and in vitro studies of transmembrane beta-strand deletion, insertion or substitution mutants of the Escherichia coli K-12 maltoporin

LamB of Escherichia coli K12, also called maltoporin, is an outer membrane protein, which specifically facilitates the diffusion of maltose and maltodextrin through the bacterial outer membrane. Each monomer is composed of an 18-stranded antiparallel beta-barrel. In the present work, on the basis of the known X-ray structure of LamB, the effects of modifications of the beta-barrel domain of maltoporin were studied in vivo and in vitro. We show that: (i) the substitution of the pair of strands beta13-beta14 of the E. coli maltoporin with the corresponding pair of strands from the functionally related maltoporin of Salmonella typhimurium yielded a protein active in vivo and in vitro; and (ii) the removal of one pair of beta-strands (deletion beta13-beta14) from the E. coli maltoporin, or its replacement by a pair of strands from the general porin OmpF of E. coli, leads to recombinant proteins that lost in vivo maltoporin activities but still kept channel formation and carbohydrate binding in vitro. We also inserted into deletion beta13-beta14 the portion of the E. coli LamB protein comprising strands beta13 to beta16. This resulted in a protein expected to have 20 beta-strands and which completely lost all LamB-specific activities in vivo and in vitro.

An amphipathic alpha-helix including glutamates 509 and 516 is crucial for membrane translocation of adenylate cyclase toxin and modulates formation and cation selectivity of its membrane channels

The Bordetella pertussis adenylate cyclase toxin-hemolysin (ACT or CyaA) is a multifunctional protein. It forms small cation-selective channels in target cell and lipid bilayer membranes and it delivers into cell cytosol the amino-terminal adenylate cyclase (AC) domain, which catalyzes uncontrolled conversion of ATP to cAMP and causes cell intoxication. Here, we demonstrate that membrane translocation of the AC domain into cells is selectively dissociated from ACT membrane insertion and channel formation when a helix-breaking proline residue is substituted for glutamate 509 (Glu-509) within a predicted transmembrane amphipathic alpha-helix. Neutral substitutions of Glu-509 had little effect on toxin activities. In contrast, charge reversal by lysine substitutions of the Glu-509 or of the adjacent Glu-516 residue reduced the capacity of the toxin to translocate the AC domain across membrane and enhanced significantly its specific hemolytic activity and channel forming capacity in lipid bilayer membranes. Combination of the E509K and E516K mutations in a single molecule further exacerbated hemolytic and channel forming activity and ablated translocation of the AC domain into cells. The lysine substitutions strongly decreased the cation selectivity of the channels, indicating that Glu-509 and Glu-516 are located within or close to the membrane channel. These results suggest that the structure including glutamate residues 509 and 516 is critical for AC membrane translocation and channel forming activity of ACT.

Mitochondria-derived and extra-mitochondrial human type-1 porin are identical as revealed by amino acid sequencing and electrophysiological characterisation

In mammalian cells porin channels are localised in both mitochondrial outer membranes and extra-mitochondrial membranes. We isolated mitochondria-derived porin of a human lymphoblastoid B cell line, determined its amino acid sequence and characterised its channel properties. Interestingly, the amino acid sequence of this porin preparation and, correspondingly, its electrophysiological characteristics in a reconstituted system were identical to those of 'Porin 31HL', the human type-1 porin purified from a crude membrane preparation of the same cell line using a different purification protocol. The results raise questions about targeting, insertion and orientation of human type-1 porin in different membranes.