An STS-based map of the human genome

A physical map has been constructed of the human genome containing 15,086 sequence-tagged sites (STSs), with an average spacing of 199 kilobases. The project involved assembly of a radiation hybrid map of the human genome containing 6193 loci and incorporated a genetic linkage map of the human genome containing 5264 loci. This information was combined with the results of STS-content screening of 10,850 loci against a yeast artificial chromosome library to produce an integrated map, anchored by the radiation hybrid and genetic maps. The map provides radiation hybrid coverage of 99 percent and physical coverage of 94 percent of the human genome. The map also represents an early step in an international project to generate a transcript map of the human genome, with more than 3235 expressed sequences localized. The STSs in the map provide a scaffold for initiating large-scale sequencing of the human genome.

Isolation of Clostridium difficile from the environment and contacts of patients with antibiotic-associated colitis

Clostridium difficile is the most important cause of antibiotic-associated colitis, but its epidemiology remains unknown. Using a selective medium for the isolation of C. difficile, cultures were obtained from the environment and contacts of hospitalized patients carrying C. difficile in their stools. In areas where carriers had diarrhea, 85 (9.3%) of 910 cultures of floors and other surfaces, especially those subject to fecal contamination, were positive. In areas where there were no known carriers, only 13 (2.6%) of 497 cultures of similar sites were positive (P less than 0.005). C difficile was isolated from hands and stools of asymptomatic hospital personnel, from sewage and soil, and from the home of a patient. Environmental isolates were toxigenic. C. difficile inoculated onto a floor persisted there for five months. Further studies are needed to document how often floor persisted there for five months. Further studies are needed to document how often C. difficile shed by patients with antibiotic-associated colitis is acquired by other persons and whether isolation precautions are capable of limiting the organism's spread.

Pressure provides new insights into protein folding, dynamics and structure

Hydrostatic pressure is a powerful tool for studying protein folding, and the dynamics and structure of folding intermediates. Recently, pressure techniques have opened two important fronts to aid our understanding of how polypeptides fold into highly structured conformations. The first advance is the stabilization of folding intermediates, making it possible to characterize their structures and dynamics by different methodologies. Kinetic studies under pressure constitute the second advance, promising detailed appraisal and understanding of protein folding landscapes. The combination of these two approaches enables dissection of the roles of packing and cavities in folding, and in assembly of multimolecular structures such as protein-DNA complexes and viruses. The study of aggregates and amyloids, derived from partially folded intermediates at the junction between productive and off-pathway folding, have also been studied, promising better understanding of diseases associated with protein misfolding.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

EEG delta activity: an indicator of attention to internal processing during performance of mental tasks

In previous papers we proposed that an increase in delta EEG activity during mental tasks might be related to an increase in subjects' attention to internal processing. In this paper we have made a narrow band analysis to detect those EEG frequencies that change selectively during the performance of a mental task that requires attention to internal processing. Two different experiments were performed: (1) a difficult mental calculation task and a control stimulus with the same physical characteristics as the arithmetical symbols were presented in random order; (2) the Sternberg paradigm for the analysis of short term memory using a memory set of 5 or 3 digits was also presented in random order. Referential recordings to linked ears were obtained in all leads of the 10/20 system. In the first experiment, the increase of power from 1.56 to 5.46 Hz was observed only during the performance of the task and not during the control condition. In the Sternberg paradigm, the increase of power from 1.56 to 3.90 Hz was greater during the difficult than during the easy condition. These results support our hypothesis that an increase in delta activity may be related to attention to internal processing during the performance of a mental task.

Analysis of exosome release and its prognostic value in human colorectal cancer

A significant proportion of extracellular nucleic acids in plasma circulate highly protected in tumor-specific exosomes, but it is unclear how the release of exosomes is modulated in carcinogenesis. We quantified by cytometry exosomes in plasma of 91 colorectal cancer patients to evaluate their potential as a tumor indicator and their repercussions on diagnosis and prognosis. We examined the involvement of TSAP6, a TP53-regulated gene involved in the regulation of vesicular secretion, in levels of circulating exosomes in plasma of colorectal patients and in HCT116 TP53-(wild-type and null) human colorectal cancer cell lines. The fraction of exosomes in cancer patients was statistically higher than in healthy controls (mean rank ¼ 53.93 vs. 24.35). High levels of exosomes in plasma of patients correlated with high levels of carcino-embryonic antigen (P ¼ 0.029) and with poorly differentiated tumors (P ¼ 0.039) and tended to have shorter overall survival than patients with low levels (P ¼ 0.056). Release of exosomes did not correlate with TSAP6 expression; and regulation of TSAP6 by TP53 was not shown either in tumor samples or in HCT116 cell lines. Although it was not suggested that the TP53/TSAP6 pathway regulates the release of exosomes into the plasma of colorectal cancer patients, the level of circulating exosomes may be used as a tumor indicator, because it correlates with poor prognosis parameters and shorter survival.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

Mutant p53 aggregates into prion-like amyloid oligomers and fibrils: implications for cancer

Over 50% of all human cancers lose p53 function. To evaluate the role of aggregation in cancer, we asked whether wild-type (WT) p53 and the hot-spot mutant R248Q could aggregate as amyloids under physiological conditions and whether the mutant could seed aggregation of the wild-type form. The central domains (p53C) of both constructs aggregated into a mixture of oligomers and fibrils. R248Q had a greater tendency to aggregate than WT p53. Full-length p53 aggregated into amyloid-like species that bound thioflavin T. The amyloid nature of the aggregates was demonstrated using x-ray diffraction, electron microscopy, FTIR, dynamic light scattering, cell viabilility assay, and anti-amyloid immunoassay. The x-ray diffraction pattern of the fibrillar aggregates was consistent with the typical conformation of cross β-sheet amyloid fibers with reflexions of 4.7 Å and 10 Å. A seed of R248Q p53C amyloid oligomers and fibrils accelerated the aggregation of WT p53C, a behavior typical of a prion. The R248Q mutant co-localized with amyloid-like species in a breast cancer sample, which further supported its prion-like effect. A tumor cell line containing mutant p53 also revealed massive aggregation of p53 in the nucleus. We conclude that aggregation of p53 into a mixture of oligomers and fibrils sequestrates the native protein into an inactive conformation that is typical of a prionoid. This prion-like behavior of oncogenic p53 mutants provides an explanation for the negative dominance effect and may serve as a potential target for cancer therapy.

Vesicle-related microRNAs in plasma of nonsmall cell lung cancer patients and correlation with survival

The identification of tumour biomarkers that detect the presence of disease using noninvasive diagnostic procedures is a key part of cancer research. We determined in plasma the vesicle-related microRNA (miRNA) expression profile of nonsmall cell lung cancer (NSCLC) and evaluate whether plasma miRNAs can be both discriminating (between patients and healthy controls) and prognostic markers. 365 human miRNAs were analysed by Taqman® low-density arrays (Applied Biosystems, Foster City, CA, USA) in the plasma from 28 NSCLC patients and 20 controls. Five selected miRNAs (let-7f, miR-20b, miR-30e-3p, miR-223 and miR-301) were validated independently by real-time PCR in plasma from 78 NSCLC and 48 controls and correlated with pathologic parameters and survival. Levels of let-7f, miR-20b and miR-30e-3p were decreased in plasma vesicles of NSCLC patients. Moreover, levels of let-7f and miR-30e-3p distinguished between two groups of patients for stage of disease and therefore possibility of surgery. Plasma levels of miR-30e-3p and let-7f were associated with short disease-free survival and overall survival, respectively. NSCLC patients and healthy controls differ in vesicle-related miRNAs in plasma. Levels of let-7f and miR-30e-3p in NSCLC patients are associated with poor outcome. Thus, plasma vesicle-related miRNAs obtained by noninvasive methods could serve as circulating tumour biomarkers of discriminating and prognostic value.

Epidemiology of antibiotic-associated colitis; isolation of Clostridium difficile from the hospital environment

Clostridium difficile is the most important cause of antibiotic-associated colitis. Using selective media, it was found that contamination with this organism was common in the environment of patients in the hospital with the disease. It was often found on floors, hoppers, toilets, bedding, mops, scales and furniture. This organism was also present on these items, but less often, in areas in which patients known to carry this hardy spore-forming organism had not been detected. Air, food and walls were negative. The organism was isolated from the hands and stools of asymptomatic hospital personnel. It was also found on surfaces in a patient's home. The importance of the various sources of the organism in its spread in the hospital is not known, and further studies are needed. It is suggested that enteric isolation precautions, and careful handwashing and cleansing of potentially contaminated surfaces and objects may be worthwhile when cases of antibiotic-associated colitis are identified.

DNA converts cellular prion protein into the beta-sheet conformation and inhibits prion peptide aggregation

The main hypothesis for prion diseases proposes that the cellular protein (PrP(C)) can be altered into a misfolded, beta-sheet-rich isoform (PrP(Sc)), which in most cases undergoes aggregation. In an organism infected with PrP(Sc), PrP(C) is converted into the beta-sheet form, generating more PrP(Sc). We find that sequence-specific DNA binding to recombinant murine prion protein (mPrP-(23-231)) converts it from an alpha-helical conformation (cellular isoform) into a soluble, beta-sheet isoform similar to that found in the fibrillar state. The recombinant murine prion protein and prion domains bind with high affinity to DNA sequences. Several double-stranded DNA sequences in molar excess above 2:1 (pH 4.0) or 0.5:1 (pH 5.0) completely inhibit aggregation of prion peptides, as measured by light scattering, fluorescence, and circular dichroism spectroscopy. However, at a high concentration, fibers (or peptide aggregates) can rescue the peptide bound to the DNA, converting it to the aggregating form. Our results indicate that a macromolecular complex of prion-DNA may act as an intermediate for the formation of the growing fiber. We propose that host nucleic acid may modulate the delicate balance between the cellular and the misfolded conformations by reducing the protein mobility and by making the protein-protein interactions more likely. In our model, the infectious material would act as a seed to rescue the protein bound to nucleic acid. Accordingly, DNA would act on the one hand as a guardian of the Sc conformation, preventing its propagation, but on the other hand may catalyze Sc conversion and aggregation if a threshold level is exceeded.

Impaired lymphocyte function in depressive illness

Mood states and immunity may be related. To investigate the immune status of patients with primary depressive illness, we compared in-vitro lymphocytic responses to three different mitogens in 26 drug-free depressed patients and 20 normal controls of comparable age and sex. We observed a generalized and marked decrease in the lymphocyte mitogenic activity among the depressive group. This defect in lymphocyte function may be indicative of an impairment in cell-mediated immunity in patients with primary depressive illness.

Cytosolic-free calcium elevation in Trypanosoma cruzi is required for cell invasion

To replicate, the trypomastigote form of Trypanosoma cruzi must invade host cells. Since a role for Ca2+ in the process of cell invasion by several intracellular parasites has been postulated, changes in the intracellular Ca2+ concentration in T. cruzi trypomastigotes and in tissue culture L6E9 myoblasts during their interaction were studied at the single cell level using digital imaging fluorescence microscopy or in cell suspensions by fluorescence spectrophotometry. An increase in cytosolic Ca2+ in T. cruzi trypomastigotes was detected at the single cell level after association of the parasites with the myoblasts. Ca2+ mobilization in the host cells was also detected upon contact with trypomastigotes either at the single cell level or in cells grown in coverslips and exposed to suspensions of trypomastigotes. Pretreatment of the parasites with the Ca2+ chelators quin 2 (50 microM) or bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA, 50 microM) decreased the trypomastigotes' association to myoblasts by approximately 40 and 63%, respectively, thus indicating that an increase in intracellular Ca2+ concentration in the parasites is required for cell invasion in addition to Ca2+ mobilization in the host cells.

Treatment of antibiotic-associated Clostridium difficile colitis with oral vancomycin: comparison of two dosage regimens

PURPOSE

High-dose (500 mg orally four times daily) vancomycin is considered by many investigators to be the most effective treatment for antibiotic-associated Clostridium difficile colitis. However, a lower dosage of 125 or 150 mg given three or four times a day has become popular, has been shown to be effective, and is less expensive than the high-dose regimen. We therefore decided to compare two vancomycin dosage regimens in a randomized trial.

PATIENTS AND METHODS

The study involved 46 hospitalized patients with serious underlying diseases complicated by C. difficile diarrhea or colitis. Patients were assigned (according to a table of random numbers) to treatment with either 125 or 500 mg of vancomycin orally four times daily for an average of 10 days.

RESULTS

No significant differences in measurable responses to the two regimens were noted. There were no treatment failures. The mean duration of diarrhea after initiation of therapy was about four days, and almost all patients had no diarrhea after one week. The organism continued to be demonstrated in the stools of about 50 percent of patients for the first few weeks after completion of therapy, and nine (20 percent) patients developed a recurrence of their diarrheal illness. Vancomycin was well tolerated by all patients.

CONCLUSION

Since the dose of 125 mg appeared to be as effective as the 500-mg dose, which is more expensive, the 125-mg dose is preferred when vancomycin is used in treatment of this disease, unless the patient is critically ill.

Retrospective review of congenital heart disease in 976 dogs

BACKGROUND

Knowledge of epidemiology is important for recognition of cardiovascular malformations.

OBJECTIVE

Review the incidence of congenital heart defects in dogs in Italy and assess breed and sex predispositions.

ANIMALS

Nine hundred and seventy-six dogs diagnosed with congenital heart disease (CHD) of 4,480 dogs presented to Clinica Veterinaria Gran Sasso for cardiovascular examination from 1997 to 2010.

METHODS

A retrospective analysis of medical records regarding signalment, history, clinical examination, radiography, electrocardiography, echocardiography, angiography, and postmortem examination was performed. Breed and sex predisposition were assessed with the odds ratio test.

RESULTS

CHD was observed in 21.7% of cases. A total of 1,132 defects were observed with single defects in 832 cases (85%), 2 concurrent defects in 132 cases (14%), and 3 concurrent defects in 12 cases (1%). The most common defects were pulmonic stenosis (PS; 32.1%), subaortic stenosis (SAS; 21.3%), and patent ductus arteriosus (20.9%), followed by ventricular septal defect (VSD; 7.5%), valvular aortic stenosis (AS; 5.7%), and tricuspid dysplasia (3.1%). SAS, PS, and VSD frequently were associated with other defects. Several breed and sex predispositions were identified.

CONCLUSIONS AND CLINICAL RELEVANCE

The results of this study are in accordance with previous studies, with slight differences. The breed and sex predilections identified may be of value for the diagnosis and screening of CHD in dogs. Additionally, the relatively high percentage of concurrent heart defects emphasizes the importance of accurate and complete examinations for identification. Because these data are from a cardiology referral center, a bias may exist.

Prion-like aggregation of mutant p53 in cancer

p53 is a master regulatory protein that participates in cellular processes such as apoptosis, DNA repair, and cell cycle control. p53 functions as a homotetrameric tumor suppressor, and is lost in more than 50% of human cancers. Recent studies have suggested that the formation of mutant p53 aggregates is associated with loss-of-function (LoF), dominant-negative (DN), and gain-of-function (GoF) effects. We propose that these phenomena can be explained by a prion-like behavior of mutant p53. We discuss the shared properties of cancer and neurodegenerative diseases and how the prion-like properties of p53 aggregates offer potential targets for drug development.

Pressure dissociation and conformational drift of the beta dimer of tryptophan synthase

Micromolar solutions of tryptophan synthase beta 2 dimer dissociate into monomers in the pressure range of 800-1600 bars as shown by studies of the spectral shift of the intrinsic fluorescence and of the fluorescence polarization of dansyl conjugates. At 25 degrees C the standard change in volume on dissociation (dV0) of the holoprotein was -162 mL mol-1, and the dissociation constant at 1 bar was K0 = 3.7 10(-10) M. Pyridoxal-reduced holoprotein and apoprotein had, within 10%, the same dV0, but K0 was decreased in the reduced protein (6 X 10(-11) M) and increased in the apoprotein (3.6 X 10(-9) M). At 4 degrees C the free energy of association of the holoprotein was reduced by 1.4 kcal mol-1, but dV0 was unchanged. In all the protein forms the decompression curves differed from the respective compression curves, indicating the loss of some free energy of association following separation of the monomers. This hysteretic behavior was largest in the apoprotein and amounted to a loss of 2.6 kcal mol-1 in the free energy of association. When the pressure was rapidly raised to 2.2 kbars, half-dissociation of the reduced pyridoxal beta 2 dimer took approximately 12 min. Upon return to atmospheric pressure reassociation was complete in 2-3 min and half of the enzyme activity was regained in 10 min; pyridoxal fluorescence recovered more slowly with a biphasic course. The independent return of these properties and the hysteretic behavior indicate that subunit separation is followed by a conformational drift like that observed in lactate dehydrogenase dissociated by either pressure or temperature or in enolase dissociated by dilution.

Fibrillar aggregates of the tumor suppressor p53 core domain

Alzheimer's disease, Parkinson's disease, cystic fibrosis, prion diseases, and many types of cancer are considered to be protein conformation diseases. Most of them are also known as amyloidogenic diseases due to the occurrence of pathological accumulation of insoluble aggregates with fibrillar conformation. Some neuroblastomas, carcinomas, and myelomas show an abnormal accumulation of the wild-type tumor suppressor protein p53 either in the cytoplasm or in the nucleus of the cell. Here we show that the wild-type p53 core domain (p53C) can form fibrillar aggregates after mild perturbation. Gentle denaturation of p53C by pressure induces fibrillar aggregates, as shown by electron and atomic force microscopies, by binding of thioflavin T, and by circular dichroism. On the other hand, heat denaturation produced granular-shaped aggregates. Annular aggregates similar to those found in the early aggregation stages of alpha-synuclein and amyloid-beta were also observed by atomic force microscopy immediately after pressure treatment. Annular and fibrillar aggregates of p53C were toxic to cells, as shown by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reduction assay. Interestingly, the hot-spot mutant R248Q underwent similar aggregation behavior when perturbed by pressure or high temperature. Fibrillar aggregates of p53C contribute to the loss of function of p53 and seed the accumulation of conformationally altered protein in some cancerous cells.

The preaggregated state of an amyloidogenic protein: hydrostatic pressure converts native transthyretin into the amyloidogenic state

Protein misfolding and aggregation cause several diseases, by mechanisms that are poorly understood. The formation of amyloid aggregates is the hallmark of most of these diseases. Here, the properties and formation of amyloidogenic intermediates of transthyretin (TTR) were investigated by the use of hydrostatic pressure and spectroscopic techniques. Native TTR tetramers (T(4)) were denatured by high pressure into a conformation that exposes tryptophan residues to the aqueous environment. This conformation was able to bind the hydrophobic probe bis-(8-anilinonaphthalene-1-sulfonate), indicating persistence of elements of secondary and tertiary structure. Lowering the temperature facilitated the pressure-induced denaturation of TTR, which suggests an important role of entropy in stabilizing the native protein. Gel filtration chromatography showed that after a cycle of compression-decompression at 1 degrees C, the main species present was a tetramer, with a small population of monomers. This tetramer, designated T(4)*, had a non-native conformation: it bound more bis-(8-anilinonaphthalene-1-sulfonate) than native T(4), was less stable under pressure, and on decompression formed aggregates under mild acidic conditions (pH 5-5.6). Our data show that hydrostatic pressure converts native tetramers of TTR into an altered state that shares properties with a previously described amyloidogenic intermediate, and it may be an intermediate that lies on the aggregation pathway. This "preaggregated" state, which we call T(4)*, provides insight into the question of how a correctly folded protein may degenerate into the aggregation pathway in amyloidogenic diseases.

Bacteroides fragilis enterotoxin gene sequences in patients with inflammatory bowel disease

We identified enterotoxigenic Bacteroides fragilis in stool specimens of patients with inflammatory bowel disease and other gastrointestinal disorders. The organism was detected in 11 (13.2%) of 83 patients with inflammatory bowel disease. Of 57 patients with active disease, 19.3% were toxin positive; none of those with inactive disease had specimens positive for enterotoxigenic Bacteroides fragilis gene sequences.

Antibiotic-induced colitis implication of a toxin neutralised by Clostridium sordellii antitoxin

A toxin(s) has been demonstrated in the stools of two patients with antibiotic-associated colitis. This toxin(s) was heat-labile, was rapidly lethal for hamsters, increased vascular permeability in rabbit skin, and was cytotoxic for cells in tissue-culture. It was neutralised by Clostridium sordellii antitoxin but not by antitoxins prepared against other clostridia; Escherichia coli, and Vibrio cholerae toxins. These characteristics were identical to those of a toxin implicated in the aetiology of antibiotic-induced colitis in the hamster. One patient improved rapidly after treatment with oral vancomycin, and at the same time the toxin disappeared from the stool.

Dissociation of amyloid fibrils of alpha-synuclein and transthyretin by pressure reveals their reversible nature and the formation of water-excluded cavities

Protein misfolding and aggregation have been linked to several human diseases, including Alzheimer's disease, Parkinson's disease, and systemic amyloidosis, by mechanisms that are not yet completely understood. The hallmark of most of these diseases is the formation of highly ordered and beta-sheet-rich aggregates referred to as amyloid fibrils. Fibril formation by WT transthyretin (TTR) or TTR variants has been linked to the etiology of systemic amyloidosis and familial amyloid polyneuropathy, respectively. Similarly, amyloid fibril formation by alpha-synuclein (alpha-syn) has been linked to neurodegeneration in Parkinson's disease, a movement disorder characterized by selective degeneration of dopaminergic neurons in the substantia nigra. Here we show that consecutive cycles of compression-decompression under aggregating conditions lead to reversible dissociation of TTR and alpha-syn fibrils. The high sensitivity of amyloid fibrils toward high hydrostatic pressure (HHP) indicates the existence of packing defects in the fibril core. In addition, through the use of HHP we are able to detect differences in stability between fibrils formed from WT TTR and the familial amyloidotic polyneuropathy-associated variant V30M. The fibrils formed by WT alpha-syn were less susceptible to pressure denaturation than the Parkinson's disease-linked variants, A30P and A53T. This finding implies that fibrils of alpha-syn formed from the variants would be more easily dissolved into small oligomers by the cellular machinery. This result has physiological importance in light of the current view that the pathogenic species are the small aggregates rather the mature fibrils. Finally, the HHP-induced formation of fibrils from TTR is relatively fast (approximately 60 min), a quality that allows screening of antiamyloidogenic drugs.

Dissociation of a native dimer to a molten globule monomer. Effects of pressure and dilution on the association equilibrium of arc repressor

The monomer-dimer association reaction of Arc repressor was studied by pressure-induced dissociation and by dilution. The dissociation was measured by the decrease (red shift) in the average energy of emission of the tryptophan fluorescence. Pressure dissociation also promoted a decrease in the excited-state lifetime of the single tryptophanyl residue, Trp14. These observations suggest that Trp14 becomes exposed to an aqueous environment following dissociation. The pressure-dissociation curves were concentration dependent, with p1/2 (half-dissociation pressure) shifting to higher pressures as the concentration increased. The dissociation constant (KdO) obtained by extrapolating the pressure-dissociation curves to atmospheric pressure was similar to that determined from the dilution curve (KdO = 30 nM). An anomalous steepness of dissociation in response to dilution was observed, suggesting that conformational changes occur as a result of dissociation of Arc repressor. Binding of bis(8-anilinonaphthalene-1-sulfonate) to Arc repressor was not significantly affected by pressure dissociation, whereas thermal or urea denaturation was accompanied by a dramatic decrease in binding. These results suggest that the conformational changes that follow dissociation induced by pressure are more limited than those following denaturation. The tryptophan anisotropy decreased by about one-half, suggesting the dissociation of a globular dimer to a compact monomer. On the other hand, denaturation by urea promoted an increase in anisotropy, as expected for a random-coil conformation. Dissociated Arc has the hydrodynamic properties of a folded monomer. On the other hand, dissociated Arc has a high degree of exposure of hydrophobic side-chains, and the distribution of conformations is much broader than that in the folded dimer. These features suggest that the dissociated subunit is a molten globule. The subunit interaction was substantially increased by a single amino acid substitution (Pro8----Leu), and the free energy of stabilization amounted to -2.9 kcal/mol. This increased stability suggests that residue 8 is located in the dimer interface and that part of the tertiary and most of the quaternary structure constraints result from the interaction between the intersubunit beta-strands.