Crystal structure of a deacylation-defective mutant of penicillin-binding protein 5 at 2.3-A resolution

Penicillin-binding protein 5 (PBP 5) of Escherichia coli functions as a d-alanine carboxypeptidase, cleaving the C-terminal d-alanine residue from cell wall peptides. Like all PBPs, PBP 5 forms a covalent acyl-enzyme complex with beta-lactam antibiotics; however, PBP 5 is distinguished by its high rate of deacylation of the acyl-enzyme complex (t(12) approximately 9 min). A Gly-105 --> Asp mutation in PBP 5 markedly impairs this beta-lactamase activity (deacylation), with only minor effects on acylation, and promotes accumulation of a covalent complex with peptide substrates. To gain further insight into the catalytic mechanism of PBP 5, we determined the three-dimensional structure of the G105D mutant form of soluble PBP 5 (termed sPBP 5') at 2.3 A resolution. The structure is composed of two domains, a penicillin binding domain with a striking similarity to Class A beta-lactamases (TEM-1-like) and a domain of unknown function. In addition, the penicillin-binding domain contains an active site loop spatially equivalent to the Omega loop of beta-lactamases. In beta-lactamases, the Omega loop contains two amino acids involved in catalyzing deacylation. This similarity may explain the high beta-lactamase activity of wild-type PBP 5. Because of the low rate of deacylation of the G105D mutant, visualization of peptide substrates bound to the active site may be possible.

Galanin regulates the postnatal survival of a subset of basal forebrain cholinergic neurons

The neuropeptide galanin colocalizes with choline acetyltransferase, the synthetic enzyme for acetylcholine, in a subset of cholinergic neurons in the basal forebrain of rodents. Chronic intracerebroventricular infusion of nerve growth factor induces a 3- to 4-fold increase in galanin gene expression in these neurons. Here we report the loss of a third of cholinergic neurons in the medial septum and vertical limb diagonal band of the basal forebrain of adult mice carrying a targeted loss-of-function mutation in the galanin gene. These deficits are associated with a 2-fold increase in the number of apoptotic cells in the forebrain at postnatal day seven. This loss is associated with marked age-dependent deficits in stimulated acetylcholine release, performance in the Morris water maze, and induction of long-term potentiation in the CA1 region of the hippocampus. These data provide unexpected evidence that galanin plays a trophic role to regulate the development and function of a subset of septohippocampal cholinergic neurons.

CD40 induces apoptosis in carcinoma cells through activation of cytotoxic ligands of the tumor necrosis factor superfamily

CD40, a tumor necrosis factor (TNF) receptor (TNFR) family member, conveys signals regulating diverse cellular responses, ranging from proliferation and differentiation to growth suppression and cell death. The ability of CD40 to mediate apoptosis in carcinoma cells is intriguing given the fact that the CD40 cytoplasmic C terminus lacks a death domain homology with the cytotoxic members of the TNFR superfamily, such as Fas, TNFR1, and TNF-related apoptosis-inducing ligand (TRAIL) receptors. In this study, we have probed the mechanism by which CD40 transduces death signals. Using a trimeric recombinant soluble CD40 ligand to activate CD40, we have found that this phenomenon critically depends on the membrane proximal domain (amino acids 216 to 239) but not the TNFR-associated factor-interacting PXQXT motif in the CD40 cytoplasmic tail. CD40-mediated cytotoxicity is blocked by caspase inhibitors, such as zVAD-fmk and crmA, and involves activation of caspase 8 and caspase 3. Interestingly, CD40 ligation was found to induce functional Fas ligand, TRAIL (Apo-2L) and TNF in apoptosis-susceptible carcinoma cells and to up-regulate expression of Fas. These findings identify a novel proapoptotic mechanism which is induced by CD40 in carcinoma cells and depends on the endogenous production of cytotoxic cytokines and autocrine or paracrine induction of cell death.

Did Project 2000 nurse training change recruitment patterns or career expectations?

In the UK, Project 2000 nurse education, introduced over the last eight years, aimed to increase the professional status of nurses and enhance skills, focusing on wider community care. This paper reports some of the results from a research project conducted between 1994 and 1996, funded by the Department of Health (Project 2000 Fitness for Purpose 1996). It was hypothesized that the changes in Project 2000 training might attract those more academically qualified and lead to more rapid career progression. The results found in this study did not support either of these hypotheses and suggestions are made about the reasons for the negative findings.

Quality of care of children with chronic diseases in Alexandria, Egypt: the models of asthma, type I diabetes, epilepsy, and rheumatic heart disease. Egyptian-Italian Collaborative Group on Pediatric Chronic Diseases

OBJECTIVES

To evaluate the quality of care delivered to children suffering from index chronic diseases using specific indicators of health care delivery and to study the predictors of suboptimal quality of care (SQC) and its outcome on children.

DESIGN

Over a 9-month period, guidelines for optimal care were formulated. A specific questionnaire for every studied chronic disease was prepared in collaboration with the clinicians in charge of the diseased children (66% pediatricians and pediatric specialists and 34% adult specialists). The clinicians were asked to write the details of daily practice, ie, how these children were managed on a routine basis as well as in an emergency situation. A cross-sectional study was conducted over a 4-month period and included 953 children suffering from bronchial asthma (BA), childhood epilepsy (CE), type I diabetes mellitus (IDDM), and rheumatic heart disease (RHD). A systematic random sample of children was selected from children visiting the ambulatory settings of all children's hospitals. Every fourth child was selected on 2 randomly chosen days each week, while all diseased children admitted in the hospital settings of the children's hospitals during the study were included. A general form describing the impact of the diseases on the child was prepared. A network of clinicians was created in all children's hospitals; seminars were held during which the content validity of the questionnaire was tested. Items were evaluated for their internal consistency using the Cronbach alpha. According to the degree of adherence to the recent therapeutic guidelines concerning selected indicators of the quality of care specific to every disease, children were categorized as receiving optimal quality of care or SQC. These indicators were: the use of inhaled bronchodilators in acute asthmatic attacks in mild asthma and the use of the prophylactic drugs (inhaled sodium cromoglycate or inhaled beclomethasone) in moderate to severe chronic BA in between acute asthmatic attacks; compliance with antiepileptic drugs in epileptic children; regular performance of self-monitoring of blood glucose and/or urine testing in diabetic children; and compliance with prophylactic antibiotics in children suffering from RHD. The records of the outpatient clinics for ambulatory and hospitalized cases were reviewed to assess the degree of compliance with the prescribed management before the index visit. Sociodemographic characteristics and health care system-related predictors of SQC were analyzed via stepwise logistic regression analysis. The impact of illness on the child was assessed by 7 items which were: dependence on parents in domestic activities, level of activity compared with peers, mood compared with peers, level of socializing, degree of discomfort attributable to illness, level of physical disadvantage, and urinary incontinence. Factor analysis with Varimax rotation was performed on items related to the impact of illness. Parental satisfaction with care was rated as excellent, very good, fair, or poor. Information on school outcome was obtained by asking the caretakers whether the child was able to attend school regularly despite his sickness. Scholastic achievement was also rated as excellent, very good, good, and acceptable. Parents were asked whether the child had ever repeated a grade because of his sickness.

SETTING

Ambulatory and hospital settings of all children's hospitals in Alexandria, Egypt.

RESULTS

Only 52% of mild asthmatics were given inhaled bronchodilators during acute attacks and 6.84% of moderate to severe asthmatics were taking prophylactic drugs (inhaled sodium cromoglycate and/or inhaled beclomethasone) between acute attacks. Similarly, only 53 of 134 (39.6%) of diabetic children were regularly performing self-monitoring of blood glucose and/or urine testing. In contrast, in epileptic children, 121 of 173 (69.9%) were judged as being compliant by their managing clinicians and more than two

The imprinted antisense RNA at the Igf2r locus overlaps but does not imprint Mas1

The gene encoding the insulin-like growth-factor type-2 receptor (Igf2r) is maternally expressed and imprinted. A CpG island in Igf2r intron 2 that carries a maternal-specific methylation imprint was shown in a transgenic model to be essential for Igf2r imprinting and for the production of an antisense RNA from the paternal allele. We report here that the endogenous region2 is the promoter for this antisense RNA (named Air, for antisense Igf2r RNA) and that the 3' end lies 107,796 bp distant in an intron of the flanking, but non-imprinted, gene Mas1.

Left ventricular function and mass after orthotopic heart transplantation: a comparison of cardiovascular magnetic resonance with echocardiography

OBJECTIVE

We compared the assessment of left ventricular function and mass by M-mode echocardiography (echo) with fast breath-hold cardiovascular magnetic resonance (CMR) in patients who received orthotopic heart transplantation. We also sought to establish the reproducibility of breath-hold CMR in this patient population.

METHODS

We prospectively acquired 51 sets of echo and CMR data in 21 patients who had undergone orthotopic heart transplantation. We examined the intraobserver and interobserver reproducibility of breath-hold CMR in this group and compared it with published data. We compared the left ventricular ejection fraction (EF) and mass determined by echo with the CMR data.

RESULTS

The average time between CMR and echo was 0 +/- 7 days (mean +/- SD), the time between each set of CMR-echo data acquisition was 5.1 +/- 4.1 months. Cardiovascular magnetic resonance showed good reproducibility in this population, with intraobserver percentage variability of 2.2% +/- 2.4% for EF and 3. 2% +/- 2.7% for mass, and interobserver percentage variability of 2. 4% +/- 1.9% for EF and 2.2% +/- 1.9% for mass. The Bland-Altman limits of agreement between echo and CMR were wide for both EF (-9. 6% to 15%) and mass, irrespective of the formula used (-61.3 to 198 g for the Bennett and Evans formula, -65.4 to 196.8 g for the American Society of Echocardiography (ASE) formula, -65.3 to 181 g for the Devereux formula, and -95.2 to 64.6 g for the Teichholz formula).

CONCLUSION

Fast-acquisition CMR is reproducible in recipients of transplanted hearts. We found poor agreement with the results of echo. The choice of technique will depend on local resources as well as the clinical importance of the result. Echo remains readily available and gives rapid assessment of volumes, EF, and mass. However, the good reproducibility of CMR may make it a more suitable technique for long-term follow-up of an individual or of a study population.

An evaluation of hospital cleaning regimes and standards

A four-part study assessing cleanliness in up to 113 environmental surfaces in an operating theatre and a hospital ward is reported. Surfaces were assessed visually, using microbiological methods and ATP bioluminescence. Results from a preliminary random survey indicated variability in cleanliness. These results were then used to select sites for monitoring before and after routine cleaning, over a 14-day period. Using published microbiological and ATP specifications 70 and 76% of these sites were unacceptable after cleaning. Visual assessment was a poor indicator of cleaning efficacy with only 18% considered unacceptable. Sites most likely to fail in the ward were in the toilet and kitchen, areas which are frequently implicated in the spread of infectious intestinal disease. Operating theatre sites had lower ATP results but 61% of sites would be considered unacceptable. There was no significant difference in general microbiological or ATP results overall before and after routine cleaning. Although some important hand contact sites showed no significant difference, overall there was a significant decrease in staphylococcal and enterobacteria counts in the ward but not in the operating theatre after cleaning. The routine cleaning programmes used did not include a biocide and cleaning using a hypochlorite based sanitizer gave much lower values. The results are discussed in relation to infection control, cleaning audits and cleaning schedules: an integrated cleaning monitoring programme using ATP bioluminescence in conjunction with visual and microbiological assessments is recommended.

Electrons and X-rays gang up on the ribosome

In all cells, protein synthesis is coordinated by the ribosome, and a number of pivotal structural studies on this complex have been completed during 1999. The combined results of the X-ray crystallography and electron microscopy studies have shed new light on the mechanism of this molecular machine.

Differential screening indicates a dramatic change in mRNA profiles during grape berry ripening. Cloning and characterization of cDNAs encoding putative cell wall and stress response proteins

We used differential screening to isolate ripening-associated cDNAs from a Shiraz grape (Vitis vinifera L.) berry cDNA library. A rapid increase in the mRNA levels of a number of cDNAs not present in unripe fruit occurred in grape berries at the onset of ripening. The putative translation products of some of these clones had homologs in other species that are involved in cell wall structure. These included four proline-rich proteins, a small protein that is similar to the non-catalytic, N-terminal domain of some pectin methylesterases, and two other glutamate-rich proteins. The remainder of the clones encoded putative stress response proteins. These included two thaumatin-like proteins, a metallothionein, a transcription factor, a cytochrome P450 enzyme, and proteins induced by water, sugar, and/or cold stress in other species. Many of the homologs of the grape cDNAs thought to be involved in cell wall structure or stress-related responses also accumulate in a developmental manner in other plants. This may indicate that the grape mRNAs accumulate in response to stresses such as the storage of high concentrations of sugars and rapid cell expansion, or they may accumulate as part of the ripening developmental program.

Nasal carriage in Vietnamese children of Streptococcus pneumoniae resistant to multiple antimicrobial agents

Resistance to antimicrobial agents in Streptococcus pneumoniae is increasing rapidly in many Asian countries. There is little recent information concerning resistance levels in Vietnam. A prospective study of pneumococcal carriage in 911 urban and rural Vietnamese children, of whom 44% were nasal carriers, was performed. Carriage was more common in children <5 years old than in those >/=5 years old (192 of 389 [49.4%] versus 212 of 522 [40.6%]; P, 0.01). A total of 136 of 399 isolates (34%) had intermediate susceptibility to penicillin (MIC, 0.1 to 1 mg/liter), and 76 of 399 isolates (19%) showed resistance (MIC, >1.0 mg/liter). A total of 54 of 399 isolates (13%) had intermediate susceptibility to ceftriaxone, and 3 of 399 isolates (1%) were resistant. Penicillin resistance was 21.7 (95% confidence interval, 7.0 to 67.6) times more common in urban than in rural children (35 versus 2%; P, <0.001). More than 40% of isolates from urban children were also resistant to erythromycin, trimethoprim-sulfamethoxazole, chloramphenicol, and tetracycline. Penicillin resistance was independently associated with an urban location when the age of the child was controlled for. Multidrug resistance (resistance to three or more antimicrobial agent groups) was present in 32% of isolates overall but in 39% of isolates with intermediate susceptibility to penicillin and 86% of isolates with penicillin resistance. The predominant serotypes of the S. pneumoniae isolates were 19, 23, 14, 6, and 18. Almost half of the penicillin-resistant isolates serotyped were serotype 23, and these isolates were often multidrug resistant. This study suggests that resistance to penicillin and other antimicrobial agents is common in carriage isolates of S. pneumoniae from children in Vietnam.

Synchronous bilateral carcinoma of the breasts occurring in a young woman with a history of Langerhans' cell histiocytosis in infancy

We report the case history of a 28-year-old woman who developed synchronous bilateral carcinoma of the breasts, having been diagnosed with multisystem Langerhans' cell histiocytosis in infancy. She had been treated with vinblastine and corticosteroids for 3 years and made a full recovery without late sequelae. We review the association of Langerhans' cell histiocytosis and its treatment with subsequent malignancy, with particular reference to carcinoma of the breast, and discuss the possible causes.

The 1.8 A crystal structure and active-site architecture of beta-ketoacyl-acyl carrier protein synthase III (FabH) from escherichia coli

BACKGROUND

beta-Ketoacyl-acyl carrier protein synthase III (FabH) initiates elongation in type II fatty acid synthase systems found in bacteria and plants. FabH is a ubiquitous component of the type II system and is positioned ideally in the pathway to control the production of fatty acids. The elucidation of the structure of FabH is important for the understanding of its regulation by feedback inhibition and its interaction with drugs. Although the structures of two related condensing enzymes are known, the roles of the active-site residues have not been experimentally tested.

RESULTS

The 1.8 A crystal structure of FabH was determined using a 12-site selenium multiwavelength anomalous dispersion experiment. The active site (Cys112, His244 and Asn274) is formed by the convergence of two alpha helices and is accessed via a narrow hydrophobic tunnel. Hydrogen-bonding networks that include two tightly bound water molecules fix the positions of His244 and Asn274, which are critical for the decarboxylation and condensation reactions. Surprisingly, the His244-->Ala mutation does not affect the transacylation reaction suggesting that His244 has only a minor influence on the nucleophilicity of Cys112.

CONCLUSIONS

The histidine and asparagine active-site residues are both required for the decarboxylation step in the condensation reaction. The nucleophilicity of the active-site cysteine is enhanced by the alpha-helix dipole effect, and an oxyanion hole promotes the formation of the tetrahedral transition state.