Prestin is the motor protein of cochlear outer hair cells

The outer and inner hair cells of the mammalian cochlea perform different functions. In response to changes in membrane potential, the cylindrical outer hair cell rapidly alters its length and stiffness. These mechanical changes, driven by putative molecular motors, are assumed to produce amplification of vibrations in the cochlea that are transduced by inner hair cells. Here we have identified an abundant complementary DNA from a gene, designated Prestin, which is specifically expressed in outer hair cells. Regions of the encoded protein show moderate sequence similarity to pendrin and related sulphate/anion transport proteins. Voltage-induced shape changes can be elicited in cultured human kidney cells that express prestin. The mechanical response of outer hair cells to voltage change is accompanied by a 'gating current', which is manifested as nonlinear capacitance. We also demonstrate this nonlinear capacitance in transfected kidney cells. We conclude that prestin is the motor protein of the cochlear outer hair cell.

Crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MgATP and peptide inhibitor

The structure of a ternary complex of the catalytic subunit of cAMP-dependent protein kinase, MgATP, and a 20-residue inhibitor peptide was determined at a resolution of 2.7 A using the difference Fourier technique starting from the model of the binary complex (Knighton et al., 1991a). The model of the ternary complex was refined using both X-PLOR and TNT to an R factor of 0.212 and 0.224, respectively. The orientation of the nucleotide and the interactions of MgATP with numerous conserved residues at the active site of the enzyme are clearly defined. The unique protein kinase nucleotide binding site consists of a five-stranded antiparallel beta-sheet with the base buried in a hydrophobic site along beta-strands 1 and 2 and fixed by hydrogen bonds to the N6 amino and N7 nitrogens. The small lobe secures the nucleotide via a glycine-rich loop and by ion pairing with Lys72 and Glu91. While the small lobe fixes the nontransferable alpha- and beta-phosphates in this inhibitor complex, the gamma-phosphate is secured by two Mg2+ ions and interacts both directly and indirectly with several residues in the large lobe--Asp184, Asn171, Lys168. Asp166 is positioned to serve as a catalytic base. The structure is correlated with previous chemical evidence, and the features that distinguish this nucleotide binding motif from other nucleotide binding proteins are delineated.

Inhibition of mitochondrial proton F0F1-ATPase/ATP synthase by polyphenolic phytochemicals

Mitochondrial proton F0F1-ATPase/ATP synthase synthesizes ATP during oxidative phosphorylation. In this study, we examined the effects of several groups of polyphenolic phytochemicals on the activity of the enzyme. Resveratrol, a stilbene phytoalexin that is present in grapes and red wine, concentration-dependently inhibited the enzymatic activity of both rat brain and liver F0F1-ATPase/ATP synthase (IC(50) of 12 - 28 microM). Screening of other polyphenolic phytochemicals using rat brain F0F1-ATPase activity resulted in the following ranking potency (IC(50) in parenthesis): piceatannol (8 microM)>resveratrol (19 microM)=(-)epigallocatechin gallate (17 microM)>(-)epicatechin gallate, curcumin (45 microM)>genistein=biochanin A=quercetin=kaempferol=morin (55 - 65 microM)>phloretin=apigenin=daidzein (approx. 100 microM). Genistin, quercitrin, phloridzin, (+)catechin, (+)epicatechin, (-)epicatechin and (-)epigallocatechin had little effect at similar concentrations. Tannic acid, theaflavins (tea extract) and grape seed proanthocyanidin extract (GSPE) had IC(50) values of 5, 20 and 30 microg ml(-1), respectively. Several monophenolic antioxidants and non-phenolic compounds were ineffective at concentrations of 210 microM or higher. The inhibition of F0F1-ATPase by resveratrol and genistein was non-competitive in nature. The effects of polyphenolic phytochemicals were additive. Both resveratrol and genistein had little effect on the Na(+)/K(+)-ATPase activity of porcine cerebral cortex, whereas quercetin had similar inhibitory potency as for F0F1-ATPase. In conclusion, the ATP synthase is a target for dietary phytochemicals. This pharmacological property of these phytochemicals should be included in the examination of their health benefits as well as potential cytotoxicity.

2.2 A refined crystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MnATP and a peptide inhibitor

. The crystal structure of a ternary complex containing the catalytic subunit of cAMP-dependent protein kinase, ATP and a 20-residue inhibitor peptide was refined at a resolution of 2.2 A to an R value of 0.177. In order to identify the metal binding sites, the crystals, originally grown in the presence of low concentrations of Mg(2+), were soaked in Mn(2+). Two Mn(2+) ions were identified using an anomalous Fourier map. One Mn(2+) ion bridges the gamma- and beta-phosphates and interacts with Asp184 and two water molecules. The second Mn(2+) ion interacts with the side chains of Asn171 and Asp l84 as well as with a water molecule. Modeling a serine into the P site of the inhibitor peptide suggests a mechanism for phosphotransfer.

HIV-1 infection and AIDS: consequences for the central nervous system

Infection with the human immunodeficiency virus-1 (HIV-1) can induce severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia. After infiltrating peripheral immune competent cells, in particular macrophages, HIV-1 provokes a neuropathological response involving all cell types in the brain. HIV-1 also incites activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways and disrupt neuronal and glial function. This review will discuss recently uncovered pathologic neuroimmune and degenerative mechanisms contributing to neuronal damage induced by HIV-1 and potential approaches for development of future therapeutic intervention.

Perfluorinated compounds in coastal waters of Hong Kong, South China, and Korea

Perfluorinated compounds (PFCs), such as perfluorooctanesulfonate (PFOS) and related compounds, have recently been identified in the environment. PFOS, the terminal degradation product of many of the PFCs, has been found globally in many wildlife species, as well as open ocean waters, even in remote regions far from sources. In this study, a solid-phase extraction procedure coupled with high-performance liquid chromatography interfaced to high-resolution mass spectrometry was used to isolate, identify, and quantify small concentrations of PFCs in seawater. These techniques were applied to investigate the local sources of PFCs in several industrialized areas of Asia and provide information on how the PFCs are circulated by coastal currents. Ranges of concentrations of PFOS in coastal seawaters of Hong Kong, the Pearl River Delta, including the South China Sea, and Korea were 0.09-3.1, 0.02-12, and 0.04-730 pg/mL, respectively, while those of perfluorooctanoic acid (PFOA) were 0.73-5.5, 0.24-16, and 0.24-320 pg/mL, respectively. Potential sources of PFCs include major industrialized areas along the Pearl River Delta of southern China and major cities of Korea, which are several of the fastest growing industrial and economic regions in the world. Detectable concentrations of PFOS and PFOA in waters of southern China were similar to those in the coastal marine environment of Japan and certain regions in Korea. Concentrations of PFCs in several locations in Korean waters were 10-100-fold greater than those in the other locations on which we report here. The spatial and seasonal variations in PFC concentrations in surface seawaters in the Pearl River Delta and South China Sea indicate the strong influence of the Pearl River discharge on the magnitude and extent of PFC contamination in southern China. All of the concentrations of PFOS were less than those that would be expected to cause adverse effects to aquatic organisms or their predators except for one location in Korea adjacent to an industrialized area. Hazard quotients were from <0.001 to 0.002 for aquatic animals and ranged from <0.001 to 17 for predatory birds.

Intracellular CXCR4 signaling, neuronal apoptosis and neuropathogenic mechanisms of HIV-1-associated dementia

The mechanism(s) by which HIV-1 affects neural injury in HIV-1-associated dementia (HAD) remains unknown. To ascertain the role that cellular and viral macrophage products play in HAD neurotoxicity, we explored one potential route for neuronal demise, CXCR4. CXCR4, expressed on lymphocytes and neurons, is both a part of neural development and a co-receptor for HIV-1. Its ligand, stromal cell-derived factor-1alpha (SDF-1alpha), affects neuronal viability. GTP binding protein (G-protein) linked signaling after neuronal exposure to SDF-1alpha, virus-infected monocyte-derived macrophage (MDM) secretory products, and virus was determined. In both human and rat neurons, CXCR4 was expressed at high levels. SDF-1alpha/beta was detected predominantly in astrocytes and at low levels in MDM. SDF-1beta/beta was expressed in HAD brain tissue and upregulated in astrocytes exposed to virus infected and/or immune activated MDM conditioned media (fluids). HIV-1-infected MDM secretions, virus and SDF-1beta induced a G inhibitory (Gi) protein-linked decrease in cyclic AMP (cAMP) and increase inositol 1,4, 5-trisphosphate (IP3) and intracellular calcium. Such effects were partially blocked by antibodies to CXCR4 or removal of virus from MDM fluids. Changes in G-protein-coupled signaling correlated, but were not directly linked, to increased neuronal synaptic transmission, Caspase 3 activation and apoptosis. These data, taken together, suggest that CXCR4-mediated signal transduction may be a potential mechanism for neuronal dysfunction during HAD.

Structural framework for the protein kinase family

In this review, we have summarized the general structural features of the catalytic subunit of cAMP-dependent protein kinase, emphasizing those features that will very likely be conserved in all members of the protein kinase family. The overall secondary structure of the catalytic core will probably be conserved throughout the catalytic core, as will the active site regions associated with MgATP binding and catalysis. The mechanisms for activation and the role of protein phosphorylation are unique for each kinase. The structure of the catalytic subunit now provides a general framework for modeling other protein kinases. Although this is no substitute for a crystal structure for each protein kinase, this one structure, nevertheless, does provide major insights to the molecular organization of each of these enzymes.

Molybdenum disulfide (MoS₂) as a broadband saturable absorber for ultra-fast photonics

The nonlinear optical property of few-layered MoS₂ nanoplatelets synthesized by the hydrothermal exfoliation method was investigated from the visible to the near-infrared band using lasers. Both open-aperture Z-scan and balanced-detector measurement techniques were used to demonstrate the broadband saturable absorption property of few-layered MoS₂. To explore its potential applications in ultrafast photonics, we fabricated a passive mode locker for ytterbium-doped fibre laser by depositing few-layered MoS₂ onto the end facet of optical fiber by means of an optical trapping approach. Our laser experiment shows that few-layer MoS₂-based mode locker allows for the generation of stable mode-locked laser pulse, centered at 1054.3 nm, with a 3-dB spectral bandwidth of 2.7 nm and a pulse duration of 800 ps. Our finding suggests that few-layered MoS₂ nanoplatelets can be useful nonlinear optical material for laser photonics devices, such as passive laser mode locker, Q-switcher, optical limiter, optical switcher and so on.

Crystal structures of the myristylated catalytic subunit of cAMP-dependent protein kinase reveal open and closed conformations

Three crystal structures, representing two distinct conformational states, of the mammalian catalytic subunit of cAMP-dependent protein kinase were solved using molecular replacement methods starting from the refined structure of the recombinant catalytic subunit ternary complex (Zheng, J., et al., 1993a, Biochemistry 32, 2154-2161). These structures correspond to the free apoenzyme, a binary complex with an iodinated inhibitor peptide, and a ternary complex with both ATP and the unmodified inhibitor peptide. The apoenzyme and the binary complex crystallized in an open conformation, whereas the ternary complex crystallized in a closed conformation similar to the ternary complex of the recombinant enzyme. The model of the binary complex, refined at 2.9 A resolution, shows the conformational changes associated with the open conformation. These can be described by a rotation of the small lobe and a displacement of the C-terminal 30 residues. This rotation of the small lobe alters the cleft interface in the active-site region surrounding the glycine-rich loop and Thr 197, a critical phosphorylation site. In addition to the conformational changes, the myristylation site, absent in the recombinant enzyme, was clearly defined in the binary complex. The myristic acid binds in a deep hydrophobic pocket formed by four segments of the protein that are widely dispersed in the linear sequence. The N-terminal 40 residues that lie outside the conserved catalytic core are anchored by the N-terminal myristylate plus an amphipathic helix that spans both lobes and is capped by Trp 30. Both posttranslational modifications, phosphorylation and myristylation, contribute directly to the stable structure of this enzyme.

Next-generation sequencing and real-time quantitative PCR for minimal residual disease detection in B-cell disorders

In this study, we compared immunoglobulin heavy-chain-gene-based minimal residual disease (MRD) detection by real-time quantitative PCR (RQ-PCR) and next-generation sequencing (NGS) to assess whether NGS could overcome some limitations of RQ-PCR and further increase sensitivity, specificity, accuracy and reproducibility. In total, 378 samples from 55 patients with acute lymphoblastic leukemia (ALL), mantle cell lymphoma (MCL) or multiple myeloma (MM) were investigated for clonotype identification, clonotype identity and comparability of MRD results. Forty-five clonotypes were identified by RQ-PCR and 49 by NGS. Clonotypes identified by both tools were identical or >97% homologous in 96% of cases. Both tools were able to routinely reach a sensitivity level of 1 × E-05. A good correlation of MRD results was observed (R=0.791, P<0.001), with excellent concordance in 79.6% of cases. Few discordant cases were observed across all disease subtypes. NGS showed at least the same level of sensitivity as allele-specific oligonucleotides-PCR, without the need for patient-specific reagents. We conclude that NGS is an effective tool for MRD monitoring in ALL, MCL and MM. Prospective comparative analysis of unselected cases is required to validate the clinical impact of NGS-based MRD assessment.

Identification of the binding site for acidic phospholipids on the pH domain of dynamin: implications for stimulation of GTPase activity

It has recently been suggested that pleckstrin homology (PH) domains bind specifically to phospholipids, with phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) being most strongly bound. This observation suggests that PH domains may be responsible for membrane association of proteins in which they occur. Further, this membrane association may be regulated by enzymes that modify lipid head groups to which PH domains may bind. We have studied the binding of phospholipids to the PH domain of human dynamin, a 100 kDa GTPase that is involved in the initial stages of endocytosis. We describe a rapid method for screening PH domain/ligand interactions that gives precise binding constants. We confirm that PtdIns(4,5)P2 can bind to dynamin PH domain, although not in an aggregated state. Using NMR spectroscopy, we have mapped a specific site on the surface of dynamin PH domain of which binding of gIns(1,4,5)P3 (the head-group skeleton of PtdIns(4,5)P2) occurs. The relative affinity of acidic phospholipids for dynamin PH domain correlates with their ability to activate the GTPase of dynamin. We propose, therefore, that the interaction of these phospholipids with dynamin is likely to occur via the PH domain. Given the fact that PH domains are often found in proteins associated with GTPase activity, or in guanine nucleotide exchange factors, we suggest that one role of PH domains may be to couple phosphatidylinositol signalling to GTP hydrolysis.

A single amino acid in the SH3 domain of Hck determines its high affinity and specificity in binding to HIV-1 Nef protein

We have examined the differential binding of Hck and Fyn to HIV-1 Nef to elucidate the structural basis of SH3 binding affinity and specificity. Full-length Nef bound to Hck SH3 with the highest affinity reported for an SH3-mediated interaction (KD 250 nM). In contrast to Hck, affinity of the highly homologous Fyn SH3 for Nef was too weak (KD > 20 microM) to be accurately determined. We show that this distinct specificity lies in a variable loop, the 'RT loop', positioned close to conserved SH3 residues implicated in the binding of proline-rich (PxxP) motifs. A mutant Fyn SH3 with a single amino acid substitution (R96I) in its RT loop had an affinity (KD 380 nM) for Nef comparable with that of Hck SH3. Based on additional mutagenesis studies we propose that the selective recognition of Nef by Hck SH3 is determined by hydrophobic interactions involving an isoleucine residue in its RT loop. Although Nef contains a PxxP motif which is necessary for the interaction with Hck SH3, high affinity binding was only observed for intact Nef protein. The binding of a peptide containing the Nef PxxP motif showed > 300-fold weaker affinity for Hck SH3 than full-length Nef.

Potent urea and carbamate inhibitors of soluble epoxide hydrolases

The soluble epoxide hydrolase (sEH) plays a significant role in the biosynthesis of inflammation mediators as well as xenobiotic transformations. Herein, we report the discovery of substituted ureas and carbamates as potent inhibitors of sEH. Some of these selective, competitive tight-binding inhibitors with nanomolar K(i) values interacted stoichiometrically with the homogenous recombinant murine and human sEHs. These inhibitors enhance cytotoxicity of trans-stilbene oxide, which is active as the epoxide, but reduce cytotoxicity of leukotoxin, which is activated by epoxide hydrolase to its toxic diol. They also reduce toxicity of leukotoxin in vivo in mice and prevent symptoms suggestive of acute respiratory distress syndrome. These potent inhibitors may be valuable tools for testing hypotheses of involvement of diol and epoxide lipids in chemical mediation in vitro or in vivo systems.

Structural basis for the specific interaction of lysine-containing proline-rich peptides with the N-terminal SH3 domain of c-Crk

BACKGROUND

Proline-rich segments in the guanine nucleotide exchange factor C3G bind much more strongly to the N-terminal Src homology 3 domain (SH3-N) of the proto-oncogene product c-Crk than to other SH3 domains. The presence of a lysine instead of an arginine in the peptides derived from C3G appears to be crucial for this specificity towards c-Crk.

RESULTS

In order to understand the chemical basis of this specificity we have determined the crystal structure of Crk SH3-N in complex with a high affinity peptide from C3G (PPPALPPKKR, Kd approximately 2 microM) at 1.5 A resolution. The peptide adopts a polyproline type II helix that binds, as dictated by electrostatic complementarity, in reversed orientation relative to the orientation seen in the earliest structures of SH3-peptide complexes. A lysine in the C3G peptide is tightly coordinated by three acidic residues in the SH3 domain. In contrast, the co-crystal structure of c-Crk SH3-N and a peptide containing an arginine at the equivalent position (determined at 1.9 A resolution) reveals non-optimal geometry for the arginine and increased disorder.

CONCLUSIONS

The c-Crk SH3 domain engages in an unusual lysine-specific interaction that is rarely seen in protein structures, and which appears to be a key determinant of its unique ability to bind the C3G peptides with high affinity.

A template for the protein kinase family

The crystal structure of the catalytic subunit of cAMP-dependent protein kinase, complexed with ATP and a 20-residue inhibitor peptide, is reviewed and correlated with chemical and genetic data. The striking convergence of the structure with the biochemistry and genetics provides for the first time a molecular basis for understanding how this enzyme functions, as well as an explanation for the highly conserved residues that are scattered throughout the molecule. Because these residues probably serve a common role in all eukaryotic protein kinases, this first protein kinase structure serves as a general template for the entire family of enzymes.

Microsatellite instability in sporadic endometrial carcinoma

BACKGROUND

Recent studies have demonstrated ubiquitous somatic microsatellite mutations in some cancers of the colon, endometrium, stomach, and pancreas.

PURPOSE

Our purpose was to characterize the frequency and nature of this replication error (RER) or mutator phenotype in sporadic endometrial carcinoma.

METHODS

Formalin-fixed, paraffin-embedded normal and tumor tissues from 45 patients with sporadic endometrial cancer were screened for the RER phenotype at three microsatellite loci. To further characterize when these alterations were acquired relative to clonal expansion, the sizes of the altered microsatellites in different tumor and normal regions were determined using selective UV radiation fractionation. Approximately 150-300 histologically defined cells on stained tissue sections were covered with small ink dots, and UV irradiation was used to destroy the DNA of cells not covered by ink. Undamaged DNA from seven to 25 spots per section were extracted, then analyzed at the Mfd27, Mfd41, and Mfd47 microsatellite loci and also at the c-K-ras gene locus with individual polymerase chain reactions. Radioactively labeled amplified DNAs were analyzed by electrophoresis and autoradiography. Fisher's exact test and the logrank test were used for statistical analysis.

RESULTS

The RER positive (RER+) phenotype was detected in nine (20%) of 45 sporadic endometrial carcinomas. The topographic tissue distributions of the altered microsatellites revealed clues to their pathogenesis. The RER+ phenotype was homogeneously present in the primary tumors and their metastases and was absent from adjacent normal and hyperplastic endometrium. The altered microsatellites were predominantly the same sizes throughout five tumors but demonstrated greater intratumor heterogeneity in three tumors. In one case, the primary tumor was stable but its metastasis was unstable. Mutant c-K-ras alleles were significantly more frequent in RER+ (56%) than in RER negative (RER-) (14%) tumors (P = .0165) and appeared to be acquired after the RER+ phenotype in one tumor. There were no significant clinical differences between the RER+ and RER- tumors.

CONCLUSIONS AND IMPLICATIONS

The RER+ phenotype is frequently present in sporadic endometrial cancers and is expressed before and during clonal expansion. The underlying mutator mutations are probably heterogeneous, since the RER+ phenotypes were diverse. The absence of altered microsatellites in adjacent normal endometrium demonstrates that the expression of the RER+ phenotype is limited to neoplastic tissue. The bulk of the microsatellite alterations appeared to be acquired prior to clonal expansion, suggesting that expression of the underlying genomic instability contributes to, and is not a consequence of, transformation.

Suppression of inflammatory neurotoxins by highly active antiretroviral therapy in human immunodeficiency virus-associated dementia

A human immunodeficiency virus type 1 (HIV)-seropositive, antiretroviral-naive patient presented with significant cognitive dysfunction. Neuropsychologic, neuroradiologic, immunologic, and virologic studies confirmed HIV-associated dementia (HAD). After 12 weeks of highly active antiretroviral therapy (HAART) with ibuprofen, dramatic improvements were demonstrated in neurologic function and were sustained for > 1 year. HIV-1 RNA in cerebrospinal fluid (CSF) decreased from 10(5) to 10(4) copies/mL after 4 weeks. After 20 weeks of therapy, plasma viremia decreased from 10(6) copies/mL to undetectable (< 96 copies/mL). Assays of neurotoxins (tumor necrosis factor-alpha, quinolinic acid, and nitric oxide) in plasma and CSF were considerably elevated at presentation and significantly decreased after therapy. Baseline plasma and CSF demonstrated neurotoxic activities in vitro, which also reduced markedly. These data, taken together, support the notion that HAD is a reversible metabolic encephalopathy fueled by viral replication. HAART used with nonsteroidal antiinflammatory agents leads to the suppression of inflammatory neurotoxins and can markedly improve neurologic function in HAD.

Membrane receptors for estrogen, progesterone, and testosterone in the rat brain: fantasy or reality

1. There are numerous circumstantial evidence supporting the concept that steroid hormones control cellular function by means other than the nuclear receptor steroid binding mechanism. It is the intent of this report to present evidence indicating that steroids bind to specific sites in neuronal membranes. 2. Some of the criteria to define steroid membrane receptors using steroid-BSA conjugates that can be radioiodinated to desired specific activity have been fulfilled for each of the three sex steroids using crude synaptosomal membrane preparations (P2 fractions) from the CNS of female and male rats. Ligand binding for each of the three steroids indicate high-affinity and high-capacity sites with distinct brain selectivity and stereospecificity. For example, 17 beta-E-6-[125I]BSA binds hypothalamic P2 fractions (HYP-P2) with an estimated Kd of about 3 +/- 0.7 nM (X +/- SE; n = 3), whereas the cerebellum P2 (CB-P2) fractions bind the ligand with a Kd of 34 +/- 7 nM and, a Bmax of 3 and 42 pmol/mg protein, respectively. Estrogen and testosterone binding fit best a one-single site, while progesterone binding sites can be best represented by a two-binding site, one high-affinity (Kd = 1-2 nM) and one low affinity (Kd = 62 nM), in CB-P2 fractions from intact adult female rat brain. Kinetics studies for T-3-[125I]BSA indicate that the estimated Kd of 30 +/- 2 nM for the olfactory bulb P2 fractions (OB-P2) from male rats is in good agreement with Kd values computed from Scatchard-derived data using the LIGAND algorithm. 3. 17 beta-E-6-[125I]BSA binding sites are stereospecific and appears to be present as early as 5 days of age in both the OB- and the CB-P2 fractions without changes during development. In contrast, P-6-[125I]BSA binding sites are practically absent during days 5 and 12 and appear by day 22. 4. Finally, membrane receptor molecules for estrogen and progesterone have been isolated and purified by affinity chromatography and characterized by PAGE and Western blot. Microsequencing of one of the membrane estrogen binding proteins indicates that the high-affinity site corresponds to the OSCP subunit of the proton ATP synthase. 5. It remains to be determined if P and T also bind to this complex enzyme or if they bind to other subunits of the family of proton ATPases. Overall the data indicate that steroid hormones conjugated to BSA are important tools to study the "reality of membrane steroid receptors."

Role of type III secretion in Edwardsiella tarda virulence

Edwardsiella tarda is a Gram-negative enteric bacterium affecting both animals and humans. Recently, a type III secretion system (TTSS) was found in Ed. tarda. Such systems are generally used by bacterial pathogens to deliver virulence factors into host cells to subvert normal cell functions. Genome-walking was performed from the eseB and esrB genes (homologues of Salmonella sseB and ssrB, respectively) identified in previous studies, to determine the sequences of the TTSS. Thirty-five ORFs were identified which encode the TTSS apparatus, chaperones, effectors and regulators. Mutants affected in genes representing each category were generated and found to have decreased survival and growth in fish phagocytes. LD50 values of the mutants were increased by at least 10-fold in comparison to those of the wild-type strain. The adherence and invasion rates of the esrA and esrB mutants were enhanced while those of the other mutants remained similar to the wild-type. The eseC and eseD mutants showed slight autoaggregation in Dulbecco's Modified Eagle Medium, whereas the rest of the mutants failed to autoaggregate. Regulation of the TTSS was found to involve the two-component regulatory system esrA–esrB. This study showed that the TTSS is important for Ed. tarda pathogenesis. An understanding of this system will provide greater insight into the virulence mechanisms of this bacterial pathogen.

Determinants of drug delivery and transport to solid tumors

This presentation addresses the barriers and determinants and the importance of drug-induced apoptosis in drug transport and delivery to organs and solid tumors. In particular, we examined the roles of interstitial space, drug removal by capillaries, tissue structure and tissue composition on drug distribution. Drug transport in bladder tissues is described by the distributed model which combined monodimensional Fickian diffusion and first order removal of drug by the perfusing blood. Microscopic evaluation of the spatial drug distribution in bladder, prostate and tongue indicates heterogeneous drug distribution with large and erratic concentration gradient. In general, drug distribution favors interstitial space and vasculature, with little penetration in muscles. Drug penetration into 3-dimensional solid tumors is typically 5- to 10-fold slower than in monolayer cultures. The transport of highly protein-bound drugs such as paclitaxel and doxorubicin in a solid tumor is retarded by a high tumor cell density and enhanced by drug-induced apoptosis. Accordingly, the delivery of a highly protein-bound drug to cells in a solid tumor is affected by its apoptotic effects and is therefore determined by the drug concentration and the treatment duration, i.e. treatment schedule. Under in vitro and in vivo conditions, the delivery of highly protein-bound drugs to tumor can be enhanced by using a pretreatment that induces apoptosis and reduction in cell density, and by using treatment schedules designed to take advantage of these drug-induced changes in tumor tissue composition. In conclusion, in addition to the usual processes involved in drug transport such as distribution through vascular space, transport across microvessel walls, and diffusion through interstitial space in tumor tissue, other factors including tissue structure and composition and alteration by drug-induced apoptosis are important determinants of drug distribution in organs and solid tumors.

Structural basis of the recognition of the dishevelled DEP domain in the Wnt signaling pathway

The DEP domain of Dishevelled (Dvl) proteins transduces signals to effector proteins downstream of Dvl in the Wnt pathway. Here we report that DEP-containing mutants inhibit Wnt-induced, but not Dvl-induced, activation of the transcription factor Lef-1. This inhibitory effect is weakened by a K434M mutation. Nuclear magnetic resonance spectroscopy revealed that the DEP domain of mouse Dvl1 comprises a three-helix bundle, a beta-hairpin 'arm' and two short beta-strands at the C-terminal region. Lys 434 is located at the tip of the beta-hairpin 'arm'. Based on our findings, we conclude that DEP interacts with regulators upstream of Dvl via a strong electric dipole on the molecule's surface created by Lys 434, Asp 445 and Asp 448; the electric dipole and the putative membrane binding site are at two different locations.

Physiological signals and oncogenesis mediated through Crk family adapter proteins

The viral Crk oncogene (v-Crk) is known to induce sarcomas in chicken and its cellular homologs c-Crk I, c-Crk II, and Crk-like (CRKL) have been implicated in many signal transduction events. These include cell differentiation, cell migration, and the induced nonresponsiveness of T-cells to stimulation of the T-cell receptor (TCR), a state known as anergy. CRKL is also the most prominent substrate of the Bcr-Abl oncoprotein which causes human chronic myelogenous leukemias (CML). The modular composition of the Crk family adapters which largely consist of Src homology (SH2 and SH3) domains has prompted an intensive search for physiological and pathological upstream and downstream signalling partners which selectively bind to these adapters. Upstream proteins include various receptors and large multisite docking proteins, while several protein kinases and guanine nucleotide release proteins (GNRPs) have been suggested to function downstream of c-Crk and CRKL. Most Crk/CRKL SH2- and SH3-binding proteins contain several docking sites with considerable sequence similarity. Thus the binding requirements of Crk/CRKL SH2 and SH3 domains are now well defined, providing a basis for the design of small inhibitory molecules to block the function of these adapter proteins. The enzymatic cascades activated through Crk family adapters are only partially known, but stress kinases (SAPKs/JNKs) and the GTPase Rap1, as well as the B-Raf isoform of the Raf protein kinases, are affected in some systems. Several yet unidentified, highly selective Crk interacting proteins detectable in specific cell types remain to be studied. More detailed analyses of the enzymatic activities triggered through Crk-type adapters will also be crucial to fully define the signalling pathways controlled by this protein family.

Selectivity changes during activation of mutant Shaker potassium channels

Mutations of the pore-region residue T442 in Shaker channels result in large effects on channel kinetics. We studied mutations at this position in the backgrounds of NH2-terminal-truncated Shaker H4 and a Shaker -NGK2 chimeric channel having high conductance (Lopez, G.A., Y.N. Jan, and L.Y. Jan. 1994. Nature (Lond.). 367: 179-182). While mutations of T442 to C, D, H, V, or Y resulted in undetectable expression in Xenopus oocytes, S and G mutants yielded functional channels having deactivation time constants and channel open times two to three orders of magnitude longer than those of the parental channel. Activation time courses at depolarized potentials were unaffected by the mutations, as were first-latency distributions in the T442S chimeric channel. The mutant channels show two subconductance levels, 37 and 70% of full conductance. From single-channel analysis, we concluded that channels always pass through the larger subconductance state on the way to and from the open state. The smaller subconductance state is traversed in approximately 40% of activation time courses. These states apparently represent kinetic intermediates in channel gating having voltage-dependent transitions with apparent charge movements of approximately 1.6 e0. The fully open T442S chimeric channel has the conductance sequence Rb+ > NH4+ > K+. The opposite conductance sequence, K+ > NH4+ > Rb+, is observed in each of the subconductance states, with the smaller subconductance state discriminating most strongly against Rb+.