The crystal structure of the asymmetric GroEL-GroES-(ADP)7 chaperonin complex

Chaperonins assist protein folding with the consumption of ATP. They exist as multi-subunit protein assemblies comprising rings of subunits stacked back to back. In Escherichia coli, asymmetric intermediates of GroEL are formed with the co-chaperonin GroES and nucleotides bound only to one of the seven-subunit rings (the cis ring) and not to the opposing ring (the trans ring). The structure of the GroEL-GroES-(ADP)7 complex reveals how large en bloc movements of the cis ring's intermediate and apical domains enable bound GroES to stabilize a folding chamber with ADP confined to the cis ring. Elevation and twist of the apical domains double the volume of the central cavity and bury hydrophobic peptide-binding residues in the interface with GroES, as well as between GroEL subunits, leaving a hydrophilic cavity lining that is conducive to protein folding. An inward tilt of the cis equatorial domain causes an outward tilt in the trans ring that opposes the binding of a second GroES. When combined with new functional results, this negative allosteric mechanism suggests a model for an ATP-driven folding cycle that requires a double toroid.

Reactions of electron-deficient alkynes and allenes under phosphine catalysis

The development of some new synthetic reactions derived from nucleophilic addition of phosphines to electron-deficient carbon-carbon triple bonds is described. These reactions show that the phosphine plays the role of a nucleophile as well as an excellent leaving group. The central problem is to generate a 1,3-dipole from alkynoates or allenoates (2,3-butadienoates) by interaction with various phosphines. This study illuminates the unusual phenomena and shows how this understanding allows control of the reaction.

Mutations in SCN9A, encoding a sodium channel alpha subunit, in patients with primary erythermalgia

Primary erythermalgia is a rare autosomal dominant disease characterised by intermittent burning pain with redness and heat in the extremities. A previous study established the linkage of primary erythermalgia to a 7.94 cM interval on chromosome 2q, but the causative gene was not identified. We performed linkage analysis in a Chinese family with primary erythermalgia, and screened the mutations in the two candidate genes, SCN9A and GCA, in the family and a sporadic patient. Linkage analysis yielded a maximum lod score of 2.11 for both markers D2S2370 and D2S2330. Based on critical recombination events in two patients in the family, we further limited the genetic region to 5.98 cM between D2S2370 and D2S2345. We then identified two missense mutations in SCN9A in the family (T2573A) and the sporadic patient (T2543C). Our data suggest that mutations in SCN9A cause primary erythermalgia. SCN9A, encoding a voltage-gated sodium channel alpha subunit predominantly expressed in sensory and sympathetic neurones, may play an important role in nociception and vasomotor regulation.

IRES-dependent second gene expression is significantly lower than cap-dependent first gene expression in a bicistronic vector

The internal ribosome entry site (IRES) has been widely used to coexpress heterologous gene products by a message from a single promoter. However, little is known about the efficiency of IRES-dependent second gene expression in comparison with that of first gene expression. This study was undertaken to characterize the relative expression of IRES-dependent second gene in a bicistronic vector, which was derived from the 5' untranslated regions of the encephalomyocarditis virus (EMCV). IRES-dependent second gene expression was compared with cap-dependent first gene expression in several cultured cell lines and in mouse liver in vivo. The expression of the IRES-dependent second gene ranged from 6 to 100% (in most cases between 20 and 50%) that of the first gene. Second gene expression in a plasmid without the IRES was 0.1-0.8% (with some exceptions) that of the first gene. These findings have important implications for the use of IRES, i.e., care should be taken regarding the decreased capacity of IRES-dependent downstream gene expression as well as in determining which gene should be positioned as the first or second gene in a bicistronic vector.

Structure and function in GroEL-mediated protein folding

Recent structural and biochemical investigations have come together to allow a better understanding of the mechanism of chaperonin (GroEL, Hsp60)-mediated protein folding, the final step in the accurate expression of genetic information. Major, asymmetric conformational changes in the GroEL double toroid accompany binding of ATP and the cochaperonin GroES. When a nonnative polypeptide, bound to one of the GroEL rings, is encapsulated by GroES to form a cis ternary complex, these changes drive the polypeptide into the sequestered cavity and initiate its folding. ATP hydrolysis in the cis ring primes release of the products, and ATP binding in the trans ring then disrupts the cis complex. This process allows the polypeptide to achieve its final native state, if folding was completed, or to recycle to another chaperonin molecule, if the folding process did not result in a form committed to the native state.

Increased expression of neurofilament subunit NF-L produces morphological alterations that resemble the pathology of human motor neuron disease

Excessive accumulation of neurofilaments in the cell bodies and proximal axons of motor neurons is a major pathological hallmark during the early stages of many human motor neuron diseases. To test directly the consequence of overexpression of the major neurofilament subunit NF-L, we produced transgenic mice that accumulate NF-L to approximately 4-fold the normal level in the sciatic nerve. In young animals, the motor neurons of the ventral horn of the spinal cord have massive accumulations of neurofilaments, swollen perikarya, and eccentrically localized nuclei. NF-L accumulation is accompanied by an increased frequency of axonal degeneration, proximal axon swelling, and severe skeletal muscle atrophy. These data indicate that extensive accumulation of neurofilaments in motor neurons can trigger the neurodegenerative process.

Disruption of signaling by Yersinia effector YopJ, a ubiquitin-like protein protease

Homologs of the Yersinia virulence effector YopJ are found in both plant and animal bacterial pathogens, as well as plant symbionts. These YopJ family members were shown to act as cysteine proteases. The catalytic triad of the protease was required for inhibition of the mitogen-activated protein kinase (MAPK) and nuclear factor kappaB (NF-kappaB) signaling in animal cells and for induction of localized cell death in plants. The substrates for YopJ were shown to be highly conserved ubiquitin-like molecules, which are covalently added to numerous regulatory proteins. YopJ family members exert their pathogenic effect on cells by disrupting this posttranslational modification.

Effects of a naturally occurring mutation in the hepatitis B virus basal core promoter on precore gene expression and viral replication

The basal core promoter (BCP) of hepatitis B virus (HBV) controls the transcription of both the precore RNA and the core RNA. The precore RNA codes for the secreted e antigen, while the core RNA codes for the major core protein and the DNA polymerase and also is the pregenomic RNA. The double mutation of nucleotides 1762 and 1764 in the BCP from A and G to T and A, respectively, is frequently observed in HBV sequences isolated from chronic patients. Several papers have reported conflicting results regarding whether this double mutation is important for e antigen expression. In order to address this issue, we have introduced this double mutation into the HBV genome and studied its effects on HBV gene expression and replication. Our results indicate that the mutated BCP can no longer bind a liver-enriched transcription factor(s) and that the transcription of only precore RNA and, consequently, the expression of e antigen were reduced. The reduction of precore gene expression was accompanied by an increase in progeny virus production. This increase was found to occur at or immediately prior to the encapsidation of the pregenomic RNA. Thus, the results of our in vitro study resolve the discrepancy of previous clinical observations and indicate that this double mutation suppresses but does not abolish the e antigen phenotype. The implications of these findings in the pathogenesis of HBV are discussed.

Distinct actions of cis and trans ATP within the double ring of the chaperonin GroEL

The chaperonin GroEL is a double-ring structure with a central cavity in each ring that provides an environment for the efficient folding of proteins when capped by the co-chaperone GroES in the presence of adenine nucleotides. Productive folding of the substrate rhodanese has been observed in cis ternary complexes, where GroES and polypeptide are bound to the same ring, formed with either ATP, ADP or non-hydrolysable ATP analogues, suggesting that the specific requirement for ATP is confined to an action in the trans ring that evicts GroES and polypeptide from the cis side. We show here, however, that for the folding of malate dehydrogenase and Rubisco there is also an absolute requirement for ATP in the cis ring, as ADP and AMP-PNP are unable to promote folding. We investigated the specific roles of binding and hydrolysis of ATP in the cis and trans rings using mutant forms of GroEL that bind ATP but are defective in its hydrolysis. Binding of ATP and GroES in cis initiated productive folding inside a highly stable GroEL-ATP-GroES complex. To discharge GroES and polypeptide, ATP hydrolysis in the cis ring was required to form a GroEL-ADP-GroES complex with decreased stability, priming the cis complex for release by ATP binding (without hydrolysis) in the trans ring. These observations offer an explanation of why GroEL functions as a double-ring complex.

Neurofilaments are obligate heteropolymers in vivo

Neurofilaments (NFs), composed of three distinct subunits NF-L, NF-M, and NF-H, are neuron-specific intermediate filaments present in most mature neurons. Using DNA transfection and mice expressing NF transgenes, we find that despite the ability of NF-L alone to assemble into short filaments in vitro NF-L cannot form filament arrays in vivo after expression either in cultured cells or in transgenic oligodendrocytes that otherwise do not contain a cytoplasmic intermediate filament (IF) array. Instead, NF-L aggregates into punctate or sheet like structures. Similar nonfilamentous structures are also formed when NF-M or NF-H is expressed alone. The competence of NF-L to assemble into filaments is fully restored by coexpression of NF-M or NF-H to a level approximately 10% of that of NF-L. Deletion of the head or tail domain of NF-M or substitution of the NF-H tail onto an NF-L subunit reveals that restoration of in vivo NF-L assembly competence requires an interaction provided by the NF-M or NF-H head domains. We conclude that, contrary to the expectation drawn from earlier in vitro assembly studies, NF-L is not sufficient to assemble an extended filament network in an in vivo context and that neurofilaments are obligate heteropolymers requiring NF-L and NF-M or NF-H.

Antioxidant activity of tocopherols, tocotrienols, and gamma-oryzanol components from rice bran against cholesterol oxidation accelerated by 2,2'-azobis(2-methylpropionamidine) dihydrochloride

The antioxidant activities of vitamin E (alpha-tocopherol, alpha-tocotrienol, gamma-tocopherol, and gamma-tocotrienol) and gamma-oryzanol components (cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate) purified from rice bran were investigated in a cholesterol oxidation system accelerated by 2,2'-azobis(2-methylpropionamidine) dihydrochloride. All components exhibited significant antioxidant activity in the inhibition of cholesterol oxidation. The highest antioxidant activity was found for 24-methylenecycloartanyl ferulate, and all three gamma-oryzanol components had activities higher than that of any of the four vitamin E components. Because the quantity of gamma-oryzanol is up to 10 times higher than that of vitamin E in rice bran, gamma-oryzanol may be a more important antioxidant of rice bran in the reduction of cholesterol oxidation than vitamin E, which has been considered to be the major antioxidant in rice bran. The antioxidant function of these components against cholesterol oxidation may contribute to the potential hypocholesterolemic property of rice bran.

Peptidoglycan recognition proteins: a novel family of four human innate immunity pattern recognition molecules

The innate immune system recognizes microorganisms through a series of pattern recognition receptors that are highly conserved in evolution. Insects have a family of 12 peptidoglycan recognition proteins (PGRPs) that recognize peptidoglycan, a ubiquitous component of bacterial cell walls. We report cloning of three novel human PGRPs (PGRP-L, PGRP-Ialpha, and PGRP-Ibeta) that together with the previously cloned PGRP-S, define a new family of human pattern recognition molecules. PGRP-L, PGRP-Ialpha, and PGRP-Ibeta have 576, 341, and 373 amino acids coded by five, seven, and eight exons on chromosomes 19 and 1, and they all have two predicted transmembrane domains. All mammalian and insect PGRPs have at least three highly conserved C-terminal PGRP domains located either in the extracellular or in the cytoplasmic (or in both) portions of the molecules. PGRP-L is expressed in liver, PGRP-Ialpha and PGRP-Ibeta in esophagus (and to a lesser extent in tonsils and thymus), and PGRP-S in bone marrow (and to a lesser extent in neutrophils and fetal liver). All four human PGRPs bind peptidoglycan and Gram-positive bacteria. Thus, these PGRPs may play a role in recognition of bacteria in these organs.

Expression of follicle-stimulating hormone and luteinizing hormone receptor messenger ribonucleic acids in bovine follicles during the first follicular wave

The objective of the present study was to characterize expression of mRNAs encoding FSH and LH receptors during follicular development and at different stages of the first follicular wave in cattle. Following estrus, groups of heifers (3-5 per group) were ovariectomized on the day of initiation of the first follicular wave (as determined by ultrasonography; Day 0), or on Days 2, 4, 6, 8, or 10 after initiation of the first wave. FSH and LH receptor mRNAs were detected within follicles > or = 4 mm and in some smaller follicles by in situ hybridization and were quantified by image analysis. FSH receptor mRNA was expressed in granulosa cells of all growing follicles, starting in some follicles with only one layer of granulosa cells. Irrespective of day of the follicular wave, the level of expression of FSH receptor mRNA in granulosa cells of healthy antral follicles ranging from 0.5 to 14 mm in diameter did not vary significantly with follicular size (r = 0.02, p > 0.10). Expression of LH receptor mRNA was first observed in theca interna cells of follicles shortly after antral formation. Irrespective of day of the follicular wave, the levels of LH receptor mRNA in theca interna cells of healthy antral follicles ranging from 0.5 to 14 mm increased with follicular size (r = 0.39, p < 0.01). In granulosa cells, LH receptor mRNA was expressed only in healthy follicles > 9 mm in diameter and was first observed in the dominant follicles collected on Day 4. Expression of mRNA for LH receptor, but not for FSH receptor, changed (p < 0.01) with the stage of the first follicular wave.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide dismutase is an abundant component in cell bodies, dendrites, and axons of motor neurons and in a subset of other neurons

Mutation in superoxide dismutase 1 (SOD1), a Cu/Zn enzyme that removes oxygen radicals and protects against oxidative injury, has been implicated in some cases of familial amyotrophic lateral sclerosis (FALS). As a first approach to examining the mechanism(s) through which these mutations cause specific degeneration of motor neurons, we have used immunocytochemistry to identify the distribution of SOD1 in populations of cells in the peripheral and central nervous systems. In the spinal cord, intense SOD1 immunoreactivity was present in motor neurons, interneurons, and substantia gelatinosa. In motor neurons, SOD1 immunoreactivity was abundant in perikarya, dendrites, and axons; most of this activity appeared to be free in the cytoplasm, although a portion was associated with membranous vesicles, presumably peroxisomes. Since a variety of central nervous system neurons, including pyramidal cells in cerebral cortex and neurons of the CA3 and CA4 sectors of the hippocampus, showed high immunoreactivity but are unaffected in ALS, the apparent abundance of SOD1 does not predict vulnerability of neurons to mutations in SOD1. Rather, SOD1 accumulates in many neuronal populations but is particularly abundant in motor neurons. Consistent with recent studies of FALS-linked SOD1 mutations in vitro and in transgenic mice, our findings offer further support for the view that the mutations confer a gain of adverse function. In this view, high, rather than limiting, levels of SOD1 may place motor neurons selectively at risk in FALS.

Saxagliptin given in combination with metformin as initial therapy improves glycaemic control in patients with type 2 diabetes compared with either monotherapy: a randomized controlled trial

AIM

The study aim was to evaluate the efficacy and safety of initial combination therapy with saxagliptin + metformin vs. saxagliptin or metformin monotherapy in treatment-naïve patients with type 2 diabetes (T2D) and inadequate glycaemic control.

METHODS

In this multicentre, randomized, double-blind, active-controlled phase 3 trial, 1306 treatment-naïve patients with T2D >or=18 to <or=77 years, glycosylated haemoglobin (HbA1c) >or=8 to <or=12%, fasting C-peptide concentration >or=1.0 ng/ml, body mass index <or=40 kg/m(2) were randomized to receive saxagliptin 5 mg + metformin 500 mg, saxagliptin 10 mg + metformin 500 mg, saxagliptin 10 mg + placebo or metformin 500 mg + placebo for 24 weeks. From weeks 1-5, metformin was uptitrated in 500-mg/day increments to 2000 mg/day maximum in the saxagliptin 5 mg + metformin, saxagliptin 10 mg + metformin and metformin + placebo treatment groups. The main outcome measure was HbA1c change from baseline to week 24. Selected secondary outcomes included change from baseline to week 24 in fasting plasma glucose (FPG), proportion of patients achieving HbA1c <7% and postprandial glucose area under the curve (PPG-AUC).

RESULTS

At 24 weeks, saxagliptin 5 mg + metformin and saxagliptin 10 mg + metformin demonstrated statistically significant adjusted mean decreases vs. saxagliptin 10 mg and metformin monotherapies in HbA1c (-2.5 and -2.5% vs. -1.7 and -2.0%, all p < 0.0001 vs. monotherapy) and FPG (-60 and -62 mg/dl vs. -31 and -47 mg/dl, both p < 0.0001 vs. saxagliptin 10 mg; p = 0.0002 saxagliptin 5 mg + metformin vs. metformin; p < 0.0001 saxagliptin 10 mg + metformin vs. metformin). Proportion of patients achieving an HbA1c <7% was 60.3 and 59.7%, respectively, for saxagliptin 5 mg + metformin and saxagliptin 10 mg + metformin (all p < 0.0001 vs. monotherapy). PPG-AUC was significantly reduced [-21,080 mg x min/dl (saxagliptin 5 mg + metformin) and -21,336 mg x min/dl (saxagliptin 10 mg + metformin) vs. -16,054 mg x min/dl (saxagliptin 10 mg) and -15,005 mg x min/dl (metformin), all p < 0.0001 vs. monotherapy]. Adverse event occurrence was similar across all groups. Hypoglycaemic events were infrequent.

CONCLUSION

Saxagliptin + metformin as initial therapy led to statistically significant improvements compared with either treatment alone across key glycaemic parameters with a tolerability profile similar to the monotherapy components.

The MLK family mediates c-Jun N-terminal kinase activation in neuronal apoptosis

Neuronal apoptotic death induced by nerve growth factor (NGF) deprivation is reported to be in part mediated through a pathway that includes Rac1 and Cdc42, mitogen-activated protein kinase kinases 4 and 7 (MKK4 and -7), c-Jun N-terminal kinases (JNKs), and c-Jun. However, additional components of the pathway remain to be defined. We show here that members of the mixed-lineage kinase (MLK) family (including MLK1, MLK2, MLK3, and dual leucine zipper kinase [DLK]) are expressed in neuronal cells and are likely to act between Rac1/Cdc42 and MKK4 and -7 in death signaling. Overexpression of MLKs effectively induces apoptotic death of cultured neuronal PC12 cells and sympathetic neurons, while expression of dominant-negative forms of MLKs suppresses death evoked by NGF deprivation or expression of activated forms of Rac1 and Cdc42. CEP-1347 (KT7515), which blocks neuronal death caused by NGF deprivation and a variety of additional apoptotic stimuli and which selectively inhibits the activities of MLKs, effectively protects neuronal PC12 cells from death induced by overexpression of MLK family members. In addition, NGF deprivation or UV irradiation leads to an increase in both level and phosphorylation of endogenous DLK. These observations support a role for MLKs in the neuronal death mechanism. With respect to ordering the death pathway, dominant-negative forms of MKK4 and -7 and c-Jun are protective against death induced by MLK overexpression, placing MLKs upstream of these kinases. Additional findings place the MLKs upstream of mitochondrial cytochrome c release and caspase activation.

The improved Allium/Vicia root tip micronucleus assay for clastogenicity of environmental pollutants

The meristematic mitotic cells of plant roots are appropriate and efficient cytogenetic materials for the detection of clastogenicity of environmental pollutants, especially for in situ monitoring of water contaminants. Among several cytological endpoints in these fast dividing cells, such as chromosome/chromatid aberrations, sister-chromatid exchanges and micronuclei, the most effective and simplest indicator of cytological damage is micronucleus formation. Although the Allium cepa and Vicia faba root meristem micronucleus assays (Allium/Vicia root MCN) have been used in clastogenicity studies about 12 times by various authors in the last 25 years, there is no report on the comparison of the efficiency of these two plant systems and in different cell populations (meristem and F1) of the root tip as well as under adequate recovery duration. In order to maximize the efficiency of these bioassays, the current study was designed to compare the Allium and the Vicia root MCN assays on the basis of chromosome length, peak sensitivity of the mitotic cells, and the regions of the root tip where the MCN are formed. The total length of the 2n complement of Allium chromosomes is 14.4 microns and the total length of the 2n complement of Vicia is 9.32 microns. The peak sensitivity determined by serial fixation at 12-h intervals after 100 R of X-irradiation is 44 h. The slope of the X-ray dose-response curve of Allium roots derived from the meristematic regions was lower than that derived from cells in the F1 region. Higher efficiency was also demonstrated when the MCN frequencies were scored from the F1 cells in both Allium and Vicia treated with formaldehyde (FA), mitomycin C (MMC), and maleic hydrazide (MH). The results indicated that scoring of MCN frequencies from the F1 cell region of the root tip was more efficient than scoring from the meristematic region. The X-ray linear regression dose-response curves were established in both Allium and Vicia cell systems and the coefficients of correlations, slope values were used to verify the reliability and efficiency of these two plant cell systems. Based on the dose-response slope value of 0.894 for Allium and 0.643 for Vicia, the Allium root MCN was a more efficient test system. The greater sensitivity of the Allium roots is probably due to the greater total length of the diploid complement and the higher number of metacentric chromosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification and identification of components of gamma-oryzanol in rice bran Oil

High-purity gamma-oryzanol was obtained from crude rice bran oil using a normal-phase preparative scale HPLC. A reverse-phase HPLC method was used for separating the individual components of gamma-oryzanol present in rice bran oil. Ten fractions were isolated and collected using the reverse-phase HPLC method, and their structures were identified. Identification was accomplished using GC/MS with an electron impact mass spectrum after components were transformed into trimethylsilyl ether derivatives. The 10 components of gamma-oryzanol were identified as Delta(7)-stigmastenyl ferulate, stigmasteryl ferulate, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, Delta(7)-campestenyl ferulate, campesteryl ferulate, Delta(7)-sitostenyl ferulate, sitosteryl ferulate, compestanyl ferulate, and sitostanyl ferulate. Three of these, cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, and campesteryl ferulate, were major components of gamma-oryzanol.

American ginseng (Panax quinquefolius L) reduces postprandial glycemia in nondiabetic subjects and subjects with type 2 diabetes mellitus

BACKGROUND

Despite a lack of medical evidence to support its therapeutic efficacy, the use of herbal medicine has increased considerably. Ginseng, one of the most widely used herbs, is hypothesized to play a role in carbohydrate metabolism and diabetes mellitus. We therefore undertook a preliminary short-term clinical study to assess whether American ginseng (Panax quinquefolius L) affects postprandial glycemia in humans.

DESIGN

On 4 separate occasions, 10 nondiabetic subjects (mean [+/-SD] age, 34+/-7 years; mean [+/-SD] body mass index [BMI], 25.6 +/- 3 kg/m2) and 9 subjects with type 2 diabetes mellitus (mean [+/-SD] age, 62 +/- 7 years; mean [+/-SD] BMI, 29 +/- 5 kg/m2; mean [+/-SD] glycosylated hemoglobin A1c, 0.08+/-0.005) were randomized to receive 3-g ginseng or placebo capsules, either 40 minutes before or together with a 25-g oral glucose challenge. The placebo capsules contained com flour, in which the quantity of carbohydrate and appearance matched the ginseng capsules. A capillary blood sample was taken fasting and then at 15, 30, 45, 60, 90, and 120 (only for subjects with type 2 diabetes mellitus ) minutes after the glucose challenge.

RESULTS

In nondiabetic subjects, no differences were found in postprandial glycemia between placebo and ginseng when administered together with the glucose challenge. When ginseng was taken 40 minutes before the glucose challenge, significant reductions were observed (P<.05). In subjects with type 2 diabetes mellitus, the same was true whether capsules were taken before or together with the glucose challenge (P<.05). Reductions in area under the glycemic curve were 18%+/-31% for nondiabetic subjects and 19+/-22% and 22+/-17% for subjects with type 2 diabetes mellitus administered before or together with the glucose challenge, respectively.

CONCLUSIONS

American ginseng attenuated postprandial glycemia in both study groups. For nondiabetic subjects, to prevent unintended hypoglycemia it may be important that the American ginseng be taken with the meal.

Marked increase in nitric oxide synthase mRNA in rat dorsal root ganglia after peripheral axotomy: in situ hybridization and functional studies

Using in situ hybridization, we studied nitric oxide (NO) synthase (EC 1.14.23.-) mRNA in lumbar dorsal root ganglia after peripheral transection of the sciatic nerve in rats. The effect of the NO synthase inhibitor N omega-nitro-L-arginine methyl ester on the nociceptive flexor reflex was also studied in axotomized rats. Nerve section induced a dramatic increase in number of NO synthase mRNA-positive cells in the ipsilateral dorsal root ganglia. In some of these cells the peptides galanin and/or vasoactive intestinal polypeptide and/or neuropeptide Y were also strongly up-regulated. Intravenous administration of nitro-L-arginine methyl ester blocked spinal hyperexcitability at much lower dosages in axotomized than in normal animals. The results suggest involvement of NO in the function of lumbar sensory neurons, especially after axotomy, perhaps preferentially at peripheral sites.

An inactivating point mutation in the inhibitory wedge of CD45 causes lymphoproliferation and autoimmunity

A model has been proposed for the regulation of CD45, and by homology other RPTPs, in which dimerization inhibits phosphatase activity through symmetrical interactions between an inhibitory structural wedge and the catalytic site. Here, we report the phenotype of mice with a single point mutation, glutamate 613 to arginine, that inactivates the inhibitory wedge of CD45. The CD45 E613R mutation causes polyclonal lymphocyte activation leading to lymphoproliferation and severe autoimmune nephritis with autoantibody production, resulting in death. Both homozygotes and heterozygotes develop pathology, indicating genetic dominance of CD45 E613R. The dramatic phenotype of CD45 E613R mice demonstrates the in vivo importance of negative regulation of CD45 by dimerization, supporting the model for regulation of CD45, and RPTPs in general.

beta-Amyloid-induced neuronal apoptosis requires c-Jun N-terminal kinase activation

beta-Amyloid (A beta) has been strongly implicated in the pathophysiology of Alzheimer's disease (AD), but the means by which the aggregated form of this molecule induces neuronal death have not been fully defined. Here, we examine the role of the c-Jun N-terminal kinases (JNKs) and of their substrate, c-Jun, in the death of cultured neuronal PC12 cells and sympathetic neurons evoked by exposure to aggregated A beta. The activities of JNK family members increased in neuronal PC12 cells within 2 h of A beta treatment and reached 3--4-fold elevation by 6 h. To test the role of these changes in death caused by A beta, we examined the effects of CEP-1347 (KT7515), an indolocarbazole that selectively blocks JNK activation. Inclusion of CEP-1347 (100--300 nM) in the culture medium effectively blocked the increases in cellular JNK activity caused by A beta and, at similar concentrations, protected both PC12 cells and sympathetic neurons from A beta-evoked-death. Effective protection required addition of CEP-1347 within 2 h of A beta treatment, indicating that the JNK pathway acts relatively proximally and as a trigger in the death mechanism. A dominant-negative c-Jun construct also conferred protection from A beta-evoked death, supporting a model in which JNK activation contributes to death via activation of c-Jun. Finally, CEP-1347 blocked A beta-stimulated activation of caspase-2 and -3, placing these downstream of JNK activation. These observations implicate the JNK pathway as a required element in death evoked by A beta and hence identify it as a potential therapeutic target in AD.

A dynamic model for the allosteric mechanism of GroEL

GroEL-assisted protein folding is regulated by a cycle of large coordinated domain movements in the 14-subunit double-ring assembly. The transition path between the closed (unliganded) and the open (liganded) states, calculated with a targeted molecular dynamics simulation, shows the highly complex subunit displacements required for the allosteric transition. The early downward motion of the small intermediate domain induced by nucleotide binding emerges as the trigger for the larger movements of the apical and equatorial domains. The combined twisting and upward displacement of the apical domain determined for a single subunit is accommodated easily in the heptamer ring only if its opening is concerted. This is a major source of cooperative ligand binding within a ring. It suggests also that GroEL has evolved so that the motion required for heptamer cooperativity is encoded in the individual subunits. A calculated model for a di-cis 14-subunit assembly is found to be destabilized by strong steric repulsion between the equatorial domains of the two rings, the source of negative cooperativity. The simulation results, which indicate that transient interactions along the transition path are essential for GroEL function, provide a detailed structural description of the motions that are involved in the GroEL allosteric cycle.

Mobilization of heavy metals by newer, therapeutically useful chelating agents

Four chelating agents that have been used most commonly for the treatment of humans intoxicated with lead, mercury, arsenic or other heavy metals and metalloids are reviewed as to their advantages, disadvantages, metabolism and specificity. Of these, CaNa2EDTA and dimercaprol (British anti-lewisite, BAL) are becoming outmoded and can be expected to be replaced by meso-2,3-dimercaptosuccinic acid (DMSA, succimer) for treatment of lead intoxication and by the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS, Dimaval) for treating lead, mercury or arsenic intoxication. Meso-2,3-DMSA and DMPS are biotransformed differently in humans. More than 90% of the DMSA excreted in the urine is found in the form of a mixed disulfide in which each of the sulfur atoms of DMSA is in disulfide linkage with an L-cysteine molecule. After DMPS administration, however, acyclic and cyclic disulfides of DMPS are found in the urine. The Dimaval-mercury challenge test holds great promise as a diagnostic test for mercury exposure, especially for low level mercurialism. Urinary mercury after Dimaval challenge may be a better biomarker of low level mercurialism than unchallenged urinary mercury excretion.