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In silico and in vitro studies have made progress in understanding protein-protein complex formation; however, the molecular mechanisms for their dissociation are unclear. Protein-protein complexes, lasting from microseconds to years, often involve induced-fit, challenging computational or kinetic analysis. Charybdotoxin (CTX), a peptide from the Leiurus scorpion venom, blocks voltage-gated K + -channels in a unique example of binding/unbinding simplicity. CTX plugs the external mouth of K + -channels pore, stopping K + -ion conduction, without inducing conformational changes. Conflicting with a tight binding, we show that external permeant ions enhance CTX-dissociation, implying a path connecting the pore, in the toxin-bound channel, with the external solution. This sensitivity is explained if CTX wobbles between several bound conformations, producing transient events that restore the electrical and ionic trans-pore gradients. Wobbling may originate from a network of contacts in the interaction interface that are in dynamic stochastic equilibria. These partially-bound intermediates could lead to distinct, and potentially manipulable, dissociation pathways., Competing Interests: HM, ID, HP, DN No competing interests declared, (© 2019, Moldenhauer et al.)

Neurons encode electrical signals with critically tuned voltage-gated ion channels and enzymes. Dedicated voltage sensor domains (VSDs) in these membrane proteins activate coordinately with an unresolved structural change. Such change conveys the transmembrane translocation of four positively charged arginine side chains, the voltage-sensing residues (VSRs; R1-R4). Countercharges and lipid phosphohead groups likely stabilize these VSRs within the low-dielectric core of the protein. However, the role of hydration, a sign-independent charge stabilizer, remains unclear. We replaced all VSRs and their neighboring residues with negatively charged aspartates in a voltage-gated potassium channel. The ensuing mild functional effects indicate that hydration is also important in VSR stabilization. The voltage dependency of the VSR aspartate variants approached the expected arithmetic summation of charges at VSR positions, as if negative and positive side chains faced similar pathways. In contrast, aspartates introduced between R2 and R3 did not affect voltage dependence as if the side chains moved outside the electric field or together with it, undergoing a large displacement and volumetric remodeling. Accordingly, VSR performed osmotic work at both internal and external aqueous interfaces. Individual VSR contributions to volumetric works approached arithmetical additivity but were largely dissimilar. While R1 and R4 displaced small volumes, R2 and R3 volumetric works were massive and vectorially opposed, favoring large aqueous remodeling during VSD activation. These diverse volumetric works are, at least for R2 and R3, not compatible with VSR translocation across a unique stationary charge transfer center. Instead, VSRs may follow separated pathways across a fluctuating low-dielectric septum., Competing Interests: The authors declare no conflict of interest.

Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K(+) channels discriminate K(+) over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K(+) channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K(+) channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K(+) channels, accounting for their diversity in unitary conductance., (© 2016 Naranjo et al.)

Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (r(E)) in several K-channel crystal structures. r(E) was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent r(E) estimates for MthK and Kv1.2/2.1 structures, with r(E) = 5.3-5.9 Å and r(E) = 4.5-5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (r(C)) for two electrophysiological counterparts, the large conductance calcium activated K-channel (r(C) = 2.2 Å) and the Shaker Kv-channel (r(C) = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between r(E) and r(C), produced consistent size radii of 3.1-3.7 Å and 3.6-4.4 Å for hydrated K(+) ions. These hydrated K(+) estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively.

Mammals maintain homeostatic control of their body temperature. Therefore, these organisms are expected to have adaptations that confer the ability to detect and react to both self and ambient temperature. Temperature-activated ion channels have been discovered to be the primary molecular determinants of thermosensation. The most representative group of these determinants constitutes members of the transient receptor potential superfamily, TRP, which are activated by either low or high temperatures covering the whole range of physiologically relevant temperatures. This review makes a critical assessment of existing analytical methods of temperature-activated TRP channel mechanisms using the cold-activated TRPM8 channel as a paradigm.

The transient receptor potential ion channel TRPA1 confers the ability to detect tissue damaging chemicals to sensory neurons and as a result mediates chemical nociception in vivo. Mouse TRPA1 is activated by electrophilic compounds such as mustard-oil and several physical stimuli such as cold temperature. Due to its sensory function inhibition of TRPA1 activity might provide an effective treatment against chronic and inflammatory pain. Therefore, TRPA1 has become a target for the development of analgesic drugs. 6-Methyl-5-(2-(trifluoromethyl)phenyl)-1H-indazole (Compound 31) has been identified by a chemical screen and lead optimization as an inhibitor of chemical activation of TRPA1. However, the structures or domains of TRPA1 that mediate the inhibitory effect of Compound 31 are unknown. Here, we screened 12,000 random mutant clones of mouse TRPA1 for their sensitivity to mustard-oil and the ability of Compound 31 to inhibit chemical activation by mustard-oil. In addition, we separately screened this mutant library while stimulating it with cold temperatures. We found that the single-point mutation I624N in the N-terminus of TRPA1 specifically affects the sensitivity to mustard-oil, but not to cold temperatures. This is evidence that sensitivity of TRPA1 to chemicals and cold temperatures is conveyed by separable mechanisms. We also identified five mutations located within the pore domain that cause loss of inhibition by Compound 31. This result demonstrates that the pore-domain is a regulator of chemical activation and suggests that Compound 31 might be acting directly on the pore-domain.

Several transient receptor potential (TRP) ion channels are activated with high sensitivity by either cold or hot temperatures. However, structures and mechanism that determine temperature directionality (cold versus heat) are not established. Here we screened 12,000 random mutant clones of the cold-activated mouse TRPA1 ion channel with a heat stimulus. We identified three single-point mutations that are individually sufficient to make mouse TRPA1 warm activated, while leaving sensitivity to chemicals unaffected. Mutant channels have high temperature sensitivity of voltage activation, specifically of channel opening, but not channel closing, which is reminiscent of other heat-activated TRP channels. All mutations are located in ankyrin repeat six, which identifies this domain as a sensitive modulator of thermal activation. We propose that a change in the coupling of temperature sensing to channel gating generates this sensitivity to warm temperatures. Our results demonstrate that minimal changes in protein sequence are sufficient to generate a wide diversity of thermal sensitivities in TRPA1., (Copyright © 2014 Elsevier Inc. All rights reserved.)

In recent years, the use of fluorescent glucose analogs has allowed the study of rapid transport modulation in heterogeneous cell cultures and complex tissues. However, the kinetic behavior of these tracers is not conventional. For instance, the fluorescent glucose analog 6-NBDG permeates the cell 50-100 times slower than glucose but the uptake of 6-NBDG is almost insensitive to glucose, an observation that casts doubts as to the specificity of the uptake pathway. To investigate this apparent anomaly in cultured astrocytes, which are rich in the glucose transporter GLUT1, we first estimated the kinetic parameters of 6-NBDG uptake, which were then incorporated into the kinetic model of GLUT1. The main outcome of the analysis was that 6-NBDG binds to GLUT1 with 300 times higher affinity than glucose, which explains why its uptake is not efficiently displaced by glucose. The high binding affinity of 6-NBDG also explains why cytochalasin B is less effective at inhibiting 6-NBDG uptake than at inhibiting glucose uptake. We conclude that 6-NBDG, used at low concentrations, permeates into astrocytes chiefly through GLUT1, and advise that the exofacial GLUT1 inhibitor 4,6-ethylidine-D-glucose be used, instead of glucose, as the tool of choice to confirm the specificity of 6-NBDG uptake.

A study of tumor infiltrating lymphocytes was carried out on cryostat sections of breast tumors in 27 patients using 24 monoclonal antibodies. Two types of infiltration--stromal and intraparenchymal--were identified. Certain correlations characteristic of subpopulation levels of immunocompetent cells identifiable by monoclonal antibody clusters CD8, CD22, CD38 and CD7; CD74 and CD4; CD11b and CD22, CD37 were established. The study also established a correlation between levels of immunocompetent cells infiltration (CD4+, CD7+, CD8+ and CD11b+) and tumor size and regional lymph node involvement.

We report on the case of a malignant non-Hodgkin lymphoma with primary location in the urinary bladder of an 83-year-old woman. Diagnosis was established by transurethral resection of the tumor and histological examination. No clinical signs (e.g. alterations of peripheral blood count) or tumor generalization were observed. To date only 86 cases of primary localization of lymphoma in the urinary bladder have been described, whereas secondary involvement occurs in 5.4-13% of cases.

MRI has been evaluated in a series of 26 patients, who suffered blunt cervical spine injuries at least 6 weeks previously, and had continuous clinical signs of radicular (n = 8) and medullary (n = 18) syndromes. In 6 patients MRI visualised localised posttraumatic intramedullary parenchymal changes; 5 patients had posttraumatic cord atrophies and 2 patients "traumatic" disc herniations. Besides direct traumatic lesions, pre-existing uni-, bi- or multisegmental degenerative cervical spinal stenosis must be considered because it predisposes to spinal cord injury. MRI is an important supplementary diagnostic measure after cervical spine trauma when there are clinical signs of cervical local, radicular or medullary syndromes, because intra- or extramedullary lesions can be visualised. However it must be emphasized that with present MR techniques not all "microcystic" posttraumatic spinal cord degenerations can be visualised, even if there are clear neurological signs of myelopathy or radiculopathy.

The authors report on one case of an abscess at the pyramidal apex. The 52-year old male patient presented with pareses of the fifth and seventh cranial nerves and hypacusis on the right side. After diagnostic procedures (CT-scan, carotid angiography), a tumor at the apex of the right pyramid was expected. During surgery a large encapsulated mass was found containing pus. A bacterial agent could not be isolated. The abscess bordered on the mucosal lining of the sphenoid sinus and on the cells of mastoid bone. The starting point of an abscess at the pyramidal apex is most commonly an otitis media, most frequently caused by staphylococcus. Sterile abscesses are seen in almost 20%. Of differential diagnosis on has to keep in mind other space-occupying lesions especially epidermoid or dermoid cysts.

We report on a case of an inflammatory conglomerate tumour proximal to the ileocaecal valve which resulted from ingested plum stones and after years led to abundant intestinal bleeding.

Spray drying of phenobarbital-polyvinyl pyrrolidone (PVP), phenobarbital-polyvinyl alcohol (PVA) and digoxin-PVP solutions yielded embeddings in the form of very fine powders. Depending on the drug-adjuvant ratio, the form in which the drug was embedded in the indifferent carriers was microcrystalline to radio-amorphous. In vitro studies showed that the dissolution of all the spray products was more rapid than that of the corresponding physical mixtures, and that the resulting solutions of the respective drugs were always oversaturated. The oversaturated solutions obtained from embeddings containing the amorphous forms of the difficulty soluble drugs were relatively stable. PVP inhibited the crystallization of phenobarbital to a greater extent than PVA, and led to a higher oversaturation of the drug in the resulting solutions. The in vitro release of digoxin was significantly more rapid from PVP embeddings (and tablets made from them) than from products containing digoxin in crystalline form.

Experimental studies on the effect of various micronized celluloses (Avicel PH 101 and Heweten 40) on the compressibility and the dissolution of sulphathiazole showed that the binding power of Heweten 40 is inferior to that of Avicel PH 101, whereas the mechanical strength of the tablets conforms to specifications. Referring to the dissolution rates, it can be said that the use of Heweten 40 is more advantageous.

Owing to the favourable physical conditions of the evaporation process, the technique of spray drying has been used for some time to obtain dried products from solutions, suspensions, emulsions and fluid extracts. In the pharmaceutical industry, it may be utilized as a -drying technique, -micronizing procedure, -procedure for the manufacture of polymorphic or amorphic forms of active substances, -technique for producing microcapsules and spray embeddings, -method for manufacturing direct-tablettable active substances. The technical development which ranges from spray dryers for laboratory experiments to industrial plants, and the continuous operation are favourable prerequisites for research and use on an ever greater scale.

The authors prepared a spray-dried sulphathiazole product consisting of hollow pellets, the drug being in the form of its metastable modification I (melting point, 200 degrees C). On the basis of force-time diagrams and of current parameters relative to the elasto-plastic deformability of substances intended for tabletting, the compression behaviour of the spraydried product was compared with that of sulphathiazole (modification I) tempered at 180 degrees C for 150 min. Scanning-electron-microscopic studies on tablet surfaces offered further insight into the compressibility of the spraydried product.