A functional group-guided approach to aptamers for small molecules

Aptameric receptors are important biosensor components, yet our ability to identify them depends on the target structures. We analyzed the contributions of individual functional groups on small molecules to binding within 27 target-aptamer pairs, identifying potential hindrances to receptor isolation-for example, negative cooperativity between sterically hindered functional groups. To increase the probability of aptamer isolation for important targets, such as leucine and voriconazole, for which multiple previous selection attempts failed, we designed tailored strategies focused on overcoming individual structural barriers to successful selections. This approach enables us to move beyond standardized protocols into functional group-guided searches, relying on sequences common to receptors for targets and their analogs to serve as anchors in regions of vast oligonucleotide spaces wherein useful reagents are likely to be found.

Using the technology acceptance model to explore health provider and administrator perceptions of the usefulness and ease of using technology in palliative care

BACKGROUND

Studies have shown that telehealth applications in palliative care are feasible, can improve quality of care, and reduce costs but few studies have focused on user acceptance of current technology applications in palliative care. Furthermore, the perspectives of health administrators have not been explored in palliative care and yet they are often heavily involved, alongside providers, in the coordination and use of health technologies. The study aim was to explore both health care provider and administrator perceptions regarding the usefulness and ease of using technology in palliative care.

METHODS

The Technology Acceptance Model (TAM) was used as the guiding theoretical framework to provide insight into two key determinants that influence user acceptance of technology (perceived usefulness and ease of use). Semi-structured interviews (n = 18) with health providers and administrators with experience coordinating or using technology in palliative care explored the usefulness of technologies in palliative care and recommendations to support adoption. Interview data were analyzed using inductive thematic analysis to identify common, meaningful themes.

RESULTS

Four themes were identified; themes related to perceived usefulness were: enabling remote connection and information-sharing platform. Themes surrounding ease of use included: integration with existing IT systems and user-friendly with ready access to technical support. Telehealth can enable remote connection between patients and providers to help address insufficiencies in the current palliative care environment. Telehealth, as an information sharing platform, could support the coordination and collaboration of interdisciplinary providers caring for patients with palliative needs. However, health technologies need to passively integrate with existing IT systems to enhance providers' workflow and productivity. User-friendliness with ready access to technical support was considered especially important in palliative care as patients often experience diminished function.

CONCLUSION

Participants' perspectives of technology acceptance in palliative care were largely dependent on their potential to help address major challenges in the field without imposing significant burden on providers and patients.

Exploring how virtual primary care visits affect patient burden of treatment

BACKGROUND

There is growing emphasis on the role of digital solutions in supporting chronic disease management. This has the potential to increase the burden patients experience in managing their health by offloading care from the health system to patients. This paper explores the effects of virtual visits on patient burden using an explicit framework measuring both the work patients do to care for their health and the challenges they experience that exacerbate burden.

METHODS

This mixed methods study evaluates a large pilot implementation of virtual visits (video, audio, and asynchronous messaging with providers) in primary care in Ontario, Canada. Participants were recruited using convenience sampling from patients using a virtual visit platform to complete a semi-structured interview or a survey including a free-text response. We conducted 17 interviews and reviewed 427 free text responses related to explore patients' perceived value and burden of these visits. We used qualitative analyses to map patients' feedback on their experience to the framework on patient burden.

MAIN FINDINGS

Virtual visits appear to reduce the work patients must do to manage their care by 1) improving access, convenience, and time needed for medical appointments, and 2) making it easier to access information and support for chronic disease management. Virtual visits also alleviate patients' perceived burden by improving continuity of care, experience of care, and providing some cost savings.

CONCLUSIONS

Virtual visits reduced overall patient burden of treatment by decreasing the required patient effort of managing medical appointments and monitoring their health, and by minimizing challenges experienced when accessing care. For regions that want to improve patient experience of care, virtual visits are likely to be of benefit. There is need for further research on the generalizability of the findings herein, particularly for high-needs populations under-represented such as those of low socioeconomic status and those in rural and remote locations.

P5014The NPAC score for predicting survival after incident acute myocardial infarction

Background

Risk stratification in acute myocardial infarction (AMI) is important for guiding clinical management. Current risk scores are mostly derived from clinical trials with stringent patient selection. We aimed to establish and evaluate a composite scoring system to predict short-term mortality after index episodes of AMI, independent of electrocardiography (ECG) pattern, in a large real-world cohort.

Methods

Using electronic health records, patients admitted to our regional teaching hospital (derivation cohort, n=2127) and an independent tertiary care center (validation cohort, n=1276) with index acute myocardial infarction between January 2013 and December 2017 as confirmed by principal diagnosis and laboratory findings, were identified retrospectively.

Results

Univariate logistic regression was used as the primary model to identify potential contributors to mortality. Stepwise forward likelihood ratio logistic regression revealed that neutrophil-to-lymphocyte ratio, peripheral vascular disease, age, and serum creatinine (NPAC) were significant predictors for 90-day mortality (Hosmer-Lemeshow test, P=0.21). Each component of the NPAC score was weighted by beta-coefficients in multivariate analysis. The C-statistic of the NPAC score was 0.75, which was higher than the conventional Charlson's score (C-statistic=0.63). Application of a deep learning model to our dataset improved the accuracy of classification with a C-statistic of 0.81.

Multivariate binary logistic regression Variable β Adjusted Odds ratio (95% CI) P-value Points Age ≥65 years 1.304 3.68 (2.63–5.17) <0.001 2 Peripheral vascular disease 1.109 3.03 (1.52–6.04) 0.002 2 NLRt ≥9.51 1.100 2.73 (2.12–3.51) <0.001 1 Creatinine≥109 μmol/L 1.003 3.00 (2.35–3.85) <0.001 2

NPAC deep learning model

Conclusions

The NPAC score comprised of four items from routine laboratory parameters and basic clinical information and can facilitate early identification of cases at risk of short-term mortality following index myocardial infarction. Deep learning model can serve as a gate-keeper to provide more accurate prediction to facilitate clinical decision making.

Prospective observational study protocol to investigate long-term adverse effects of methylphenidate in children and adolescents with ADHD: the Attention Deficit Hyperactivity Disorder Drugs Use Chronic Effects (ADDUCE) study

INTRODUCTION

Methylphenidate is the most frequently used medication for the treatment of attention-deficit/hyperactivity disorder (ADHD) in Europe. Following concerns about its safety, the European Commission called for research into the long-term effects of methylphenidate on children and adolescents with ADHD. The Attention Deficit Hyperactivity Disorder Drugs Use Chronic Effects (ADDUCE) research programme was designed to address this call. At the heart of this programme is a 2-year longitudinal naturalistic pharmacovigilance study being conducted in 27 European sites.

METHODS AND ANALYSIS

3 cohorts of children and adolescents (aged 6-17) living in the UK, Germany, Italy and Hungary are being recruited:Group 1 (Medicated ADHD): 800 ADHD medication-naive children and adolescents with a clinical diagnosis of ADHD about to start methylphenidate treatment for the first time.Group 2 (Unmedicated ADHD): 400 children and adolescents with a clinical diagnosis of ADHD who have never been treated with ADHD medication and have no intention of beginning medication.Group 3 (Non-ADHD): 400 children and adolescents without ADHD who are siblings of individuals in either group 1 or 2.All participants will be assessed 5 times during their 2-year follow-up period for growth and development, psychiatric, neurological and cardiovascular health. The primary outcome measure will be the height velocity SD score.

ETHICS AND DISSEMINATION

Ethical approval for the study has been granted by the East of Scotland Research Ethics Service. Following this approval, patient information leaflets and consent forms were translated as necessary and submissions made by lead sites in each of the other 3 countries to their own ethics committees. Following ethical approval in each country, local ethical permissions at each site were sought and obtained as needed. The study's website (http://www.adhd-adduce.org/page/view/2/Home) provides information for researchers, participants and the general public.

TRIAL REGISTRATION NUMBER

NCT01470261.

Time to surgery in acute rotator cufftear: A systematic review

Aims

We performed a systematic review of the literature to determine whether earlier surgical repair of acute rotator cuff tear (ARCT) leads to superior post-operative clinical outcomes.

Methods

The MEDLINE, Embase, CINAHL, Web of Science, Cochrane Libraries, controlled-trials.com and clinicaltrials.gov databases were searched using the terms: ‘rotator cuff’, or ‘supraspinatus’, or ‘infraspinatus’, or ‘teres minor’, or ‘subscapularis’ AND ‘surgery’ or ‘repair’. This gave a total of 15 833 articles. After deletion of duplicates and the review of abstracts and full texts by two independent assessors, 15 studies reporting time to surgery for ARCT repair were included. Studies were grouped based on time to surgery < 3 months (group A, seven studies), or > 3 months (group B, eight studies). Weighted means were calculated and compared using Student’s t-test.

Results

Group B had a significantly higher pre-operative Constant score (CS) (p < 0.001), range of movement in external rotation (p = 0.003) and abduction (p < 0.001) compared with group A. Both groups showed clinical improvement with surgical repair; group A had a significantly improved Constant score, University of California, Los Angeles (UCLA) shoulder score, abduction and elevation post-operatively (all p < 0.001). Group B had significantly improved Constant score (p < 0.001) and external rotation (p < 0.001) post-operatively. The mean Constant score improved by 33.5 for group A and by 27.5 for group B.

Conclusion

These findings should be interpreted with caution due to limitations and bias inherent to case-series. We suggest a trend that earlier time to surgery may be linked to better Constant score, and active range of movement in abduction and elevation. Additional prospective studies are required.

A Toll/IL-1R/resistance domain-containing thioredoxin regulates phagocytosis in Entamoeba histolytica (56.23)

Entamoeba histolytica is a parasite protozoan that infects humans and causes amebiasis in developing countries. Phagocytosis of epithelial cells, erythrocytes, leucocytes, and commensal microbiota bacteria is a major pathogenic mechanism used by this parasite. A Toll/IL-1R/Resistance (TIR) domain-containing protein is required for bacterial phagocytosis in the social ameba Dyctiostelium discoideum, both for nutrition and for protection against infection. In insects and vertebrates, TIR domain-containing proteins regulate phagocytic cell activation. Therefore, we investigated whether E. hystolytica expresses TIR domain-containing molecules that may be involved in the phagocytosis of erythrocytes and bacteria. Using Hidden Markov models (HMM), we identified an E. histolytica thioredoxin containing a TIR-like domain. The primary structure of this putative TIR domain exhibited low similitude with the TIR domain of human Toll-like Receptor (TLR)-2; however, the predicted tertiary structures of these two TIR domains were remarkably similar. Interestingly, the phagocytosis of erythrocytes and E. coli by E. histolytica trophozoites increased after the inhibition of the expression of thioredoxin using a specific siRNA. This suggests that TIR domain-containing thioredoxin is a negative regulator of phagocytosis in E. histolytica.

Educational interventions to reduce prescribing errors

OBJECTIVE

Little is known about teaching paediatricians to prescribe or about assessing their competency. This study aimed to identify educational interventions to reduce dose calculation errors.

DESIGN

Literature review, a questionnaire survey of paediatric healthcare professionals, observation and interviews were performed.

RESULTS

Literature review identified one paper describing an in-service test for medical trainees. 319/559 questionnaires were returned (57%). 34 mentioned educational interventions, 15 centres provided further information on teaching and assessment methods and 13 provided presentations, usually at doctors' induction. Many interventions had a similar format, including describing differences from adult prescribing, common errors and how to calculate doses. Paediatric clinical pharmacists play a significant role in delivering training and competency assessment.

CONCLUSION

Teaching of paediatric prescribing takes place mostly in the format of lectures during doctors' induction. Few centres assess competency and no validated tool exists. There has been little evaluation of the impact of teaching on competency to prescribe.

Medicines for children licensed by the European Medicines Agency (EMEA): the balance after 10 years

OBJECTIVE

The 1995-2005 balance of EMEA activities in the field of paediatric medicines was evaluated, taking into account the number both of drugs authorised for children and paediatric studies supporting the Marketing Authorisation (MA).

METHODS

Data on drugs authorised by EMEA were extracted from EPARs (European Public Assessment Reports). Active substance, year of approval, anatomical, therapeutic and chemical (ATC) code, indication, orphan status, ages, and registrative clinical studies characteristics were assessed.

RESULTS

The percentage of authorised substances for paediatrics is 33.3%. This percentage decreased or increased when different subsets of medicines were considered [medicines for children under 2 years (23.4%), N-ATC code drugs (6%) and orphan drugs (46.4%)]. A total of 165 trials were included in the MA dossiers of 51 drugs at the time of approval, and additional 22 studies were added to the dossiers of 12 active substances submitted for paediatric variations. PK and Efficacy/Safety studies were performed for 32 (52%) active substances, while either one PK or one Efficacy/Safety study was carried out for 43 (69%) and 45 (73%) substances, respectively.

CONCLUSIONS

This report demonstrates that the total number of paediatric medicines approved by EMEA is stable over the 10-year period, while an increase in drugs to treat serious or orphan diseases has been observed. In addition, under the Centralised Procedure, a valuable number of paediatric trials have been submitted to support drug approval.

Physical and microbiological stability of an extemporaneous tacrolimus suspension for paediatric use

OBJECTIVE

An extemporaneous suspension of tacrolimus for paediatric use has recently been developed but poor bioavailability and erratic plasma concentrations were observed during clinical use. It was not clear whether this was due to changes in the physical properties of the suspension during storage. The aim of this work was to investigate the physical and microbiological stability over the recommended 8-week shelf-life of this extemporaneous tacrolimus suspension.

METHODS

Suspensions (0.5 mg/mL) were custom made by a special manufacturer under Good Manufacturing Practice conditions. The procedure involved mixing tacrolimus capsule contents into Ora Plus and Simple Syrup (1 : 1) using a mortar and pestle followed by an homogenization step. The particle sizes of the suspensions were measured using a MasterSizer. A light microscope equipped with polarizers was used to visualize any particle size changes or crystal growth. Viable bacterial and fungal contamination was assessed using standard colony count techniques on solid media. The suspensions were kept at 22-26 degrees C and evaluated weekly.

RESULTS

The volume mean diameter d((4,3)) from laser diffraction did not change significantly. Light microscopy did not reveal any significant change in particle size or crystal growth. Contamination by viable and culturable micro-organisms could not be detected.

CONCLUSION

The suspension was physically (particle size) and microbiologically stable during the 8-week study period suggesting other factors including poor dosing could be responsible for the pharmacokinetic variation observed during clinical use which warrants further investigation.

Safety and efficacy of using the LigaSure vessel sealing system for securing the pedicles in vaginal hysterectomy: randomised controlled trial

OBJECTIVE

To assess the safety and efficacy of using the LigaSure vessel sealing system for securing the pedicles during vaginal hysterectomy in comparison with the conventional method of securing the pedicles by suture ligation.

DESIGN

Randomised controlled trial.

SETTING

Gynaecology Department, Benenden Hospital, Kent.

POPULATION

One hundred and sixteen women undergoing vaginal hysterectomy were prospectively randomised to either LigaSure (Group I) or suture ligation (Group II) for securing the pedicles.

METHODS

Data of patients were collected prospectively. Statistical analysis was performed using the Mann-Whitney U test, chi(2) and Fisher's exact test as appropriate.

MAIN OUTCOME MEASURES

Operating time, operative blood loss and peri-operative complications.

RESULTS

The operating time was significantly shorter in the LigaSure group compared with the control group (P < 0.04). There was no statistical significant difference between the two groups in operative blood loss (P= 0.433), but peri-operative haemorrhagic complications were less frequent in the LigaSure group (0%vs 6.8%, P= 0.057). Four patients in the control group required either conversion to laparotomy because of bleeding, return to theatre for immediate post-operative haemorrhage or readmission for vault haematoma, whereas none in the LigaSure group had bleeding from unsecured pedicles.

CONCLUSION

The LigaSure vessel sealing system is a safe alternative for securing pedicles in vaginal hysterectomy when compared with conventional suture ligation. Larger studies are required to determine its place in gynaecological surgery.

Pharmaceutical care for elderly patients shared between community pharmacists and general practitioners: a randomised evaluation. RESPECT (Randomised Evaluation of Shared Prescribing for Elderly people in the Community over Time) [ISRCTN16932128]

BACKGROUND

This trial aims to investigate the effectiveness and cost implications of 'pharmaceutical care' provided by community pharmacists to elderly patients in the community. As the UK government has proposed that by 2004 pharmaceutical care services should extend nationwide, this provides an opportunity to evaluate the effect of pharmaceutical care for the elderly.

DESIGN

The trial design is a randomised multiple interrupted time series. We aim to recruit 700 patients from about 20 general practices, each associated with about three community pharmacies, from each of the five Primary Care Trusts in North and East Yorkshire. We shall randomise the five resulting groups of practices, pharmacies and patients to begin pharmaceutical care in five successive phases. All five will act as controls until they receive the intervention in a random sequence. Until they receive training community pharmacists will provide their usual dispensing services and so act as controls. The community pharmacists and general practitioners will receive training in pharmaceutical care for the elderly. Once trained, community pharmacists will meet recruited patients, either in their pharmacies (in a consultation room or dispensary to preserve confidentiality) or at home. They will identify drug-related issues/problems, and design a pharmaceutical care plan in conjunction with both the GP and the patient. They will implement, monitor, and update this plan monthly. The primary outcome measure is the 'Medication Appropriateness Index'. Secondary measures include adverse events, quality of life, and patient knowledge and compliance. We shall also investigate the cost of pharmaceutical care to the NHS, to patients and to society as a whole.

Assessing the value of a leg ulcer education programme in Hong Kong

Patients with leg ulcers require expert care, but nurses do not always receive full training and education on this subject. A short education programme devised for community nurses in Hong Kong resulted in significant gains in knowledge.

Measuring the incidence of lower limb ulceration in the Chinese population in Hong Kong

OBJECTIVE

This retrospective study set out to examine the incidence, patient characteristics and current practice among patients with ulcers on the lower leg and foot who were under the care of the community nursing service of a regional hospital in Hong Kong. There is no clear differentiation between leg ulcers and foot ulcers in local practice in Hong Kong.

METHOD

The nursing records of 819 subjects receiving treatment at home from the regional hospital's community nursing service were reviewed. All were active cases on 31 October 2000.

RESULTS

The patients' median age was 76 (range: 36-100); 86% were aged over 65. Seventy-five percent of the patients had dressings changed daily, with 28 types of dressing being used. Nurses changed dressings in the patients' homes or in residential homes. Of the 94 patients with ulcers on the lower leg and foot, 75% had their dressings changed daily and only six less than three times a week. Fifty-four percent received regular podiatry clinic follow-up.

CONCLUSION

Care of patients with ulcers on the lower limb represents a considerable workload for community nurses in Hong Kong, where little attention has been paid to the problem and current treatments. The number of patients with these ulcers cared for by community nurses in Hong Kong was high, with wide variations in management. Further investigation into evidence-based practice is needed to develop clinical guidelines and protocols that will achieve quality care. Research is now required in a clinical setting and for comparison with existing wound-care products.

Parenteral drug administration errors by nursing staff on an acute medical admissions ward during day duty

BACKGROUND

Parenteral therapy is a route of administration for drugs which are poorly absorbed via the oral route and it can provide a rapid response during an emergency. However, poorly prepared and/or administered parenteral therapy can cause potential harm to patients such as thrombus formation, severe hypersensitivity reactions and infection. Very few studies have investigated the incidence of medication errors associated with parenteral drug administration.

OBJECTIVES

To determine the error rate during preparation and administration of parenteral medications by nursing staff and to propose strategies to reduce the error rate during parenteral administration.

METHODS

A direct, disguised observation technique was used. The first author (JB) observed and recorded errors that occurred during the preparation and administration of parenteral medications on an admissions ward between 8.00 am and 4.30 pm from Monday to Friday for a 4-week period during December 1998. The staff were told that the observer was timing the administration; therefore they were not aware of the true nature of the study. This study was approved by the hospital audit committee.

RESULTS

Drug administration was witnessed for a 4-week period providing 107 opportunities for error. 27 errors were observed which equated to an error rate of 25.2% [95% confidence interval (CI) 17.0 to 33.5%] including wrong time errors. Excluding wrong time errors, the most frequently occurring type of error, reduced the error rate to 10.3% (95% CI 3.8 to 14.9%).

DISCUSSION

The error rate was lower than reported in the literature, this may be due to different methodologies, small sample size or effective nursing training and operating procedures. In the observed hospital, only nursing staff who have completed a training package are allowed to administer parenteral medications.

CONCLUSION

Based on our small study, and 2 previous small studies, we can conclude that parenteral medication administration errors are common in the UK; however, these studies are too small-scale to detect rare and serious errors.

An outbreak of non-sexually transmitted gonococcal conjunctivitis in Central Australia and the Kimberley region

From 13 February to 27 June 1997, 447 cases of gonococcal conjunctivitis were identified by Communicable Disease and Public Health Centres and Community Clinics in the Northern Territory, Western Australia and South Australia. The outbreak involved Aboriginal communities predominantly in Central Australia and the Kimberley region in Western Australia. This was the first outbreak recorded in the Kimberley region. It is not yet known whether the Kimberley cases were part of the larger Central Australian outbreak or whether they represented a separate and unrelated outbreak. Environmental factors associated with this outbreak were similar to those seen in previous outbreaks. Control measures were based on early recognition and treatment of index cases and identifying and treating contacts. Until sexually transmitted Neisseria gonorrhoeae is controlled in communities gonococcal conjunctivitis is likely to appear again. The role of oropharyngeal carriage of N. gonorrhoeae needs to be evaluated further.

Intrauterine insemination: effect of the temporal relationship between the luteinizing hormone surge, human chorionic gonadotrophin administration and insemination on pregnancy rates

The optimal time period for intrauterine insemination (IUI) in relation to either luteinizing hormone (LH) surge or human chorionic gonadotrophin (HCG) administration leading to the best pregnancy rates has not been determined. In this study, 856 consecutive human menopausal gonadotrophin (HMG)-stimulated and 49 natural unstimulated IUI cycles carried out at a reproductive medicine unit affiliated with a tertiary centre were analysed in a retrospective fashion. There were three scenarios in the temporal relationship of the LH surge, HCG administration and artificial insemination. These were (group A) subjects who had an endogenous LH surge but were not given HCG; (group B) subjects who were given HCG after an observed LH surge, and (group C) subjects who were given HCG before the LH surge. The overall pregnancy rate (PR) was 16% per cycle. The PR was 9% in group A, 20% in group B and 14% in group C. The PR in group B was significantly better than group C (P = 0.04). In group B, the longer the time interval between the LH surge and HCG administration, the better the PR up to 20 h (P = 0.025); the timing of IUI based on the LH surge was not critical to the achievement of pregnancy within 3 days. In group C, PR improved with the increasing interval between HCG and IUI from <28 h up to 60 h. We conclude that a better PR is achieved if a spontaneous LH surge occurs before HCG administration, especially where the administration of HCG is delayed 8-20 h after an observed LH surge; the timing of IUI based on the LH surge is not critical to the achievement of pregnancy within 3 days.

A two-site mechanism for ATP hydrolysis by the asymmetric Rep dimer P2S as revealed by site-specific inhibition with ADP-A1F4

The Escherichia coli Rep helicase is a dimeric motor protein that catalyzes the transient unwinding of duplex DNA to form single-stranded (ss) DNA using energy derived from the binding and hydrolysis of ATP. In an effort to understand this mechanism of energy transduction, we have used pre-steady-state methods to study the kinetics of ATP binding and hydrolysis by an important intermediate in the DNA unwinding reaction--the asymmetric Rep dimer state, P2S, where ss DNA [dT(pT)15] is bound to only one subunit of the Rep dimer. To differentiate between the two potential ATPase active sites inherent in the dimer, we constructed dimers with one subunit covalently cross-linked to ss DNA and where one or the other of the ATPase sites was selectively complexed to the tightly bound transition state analog ADP-A1F4. We found that when ADP-A1F4 is bound to the Rep subunit in trans from the subunit bound to ss DNA, steady-state ATPase activity of 18 s(-1) per dimer (equivalent to wild-type P2S) was recovered. However, when the ADP-A1F4 and ss DNA are both bound to the same subunit (cis), then a titratable burst of ATP hydrolysis is observed corresponding to a single turnover of ATP. Rapid chemical quenched-flow techniques were used to resolve the following minimal mechanism for ATP hydrolysis by the unligated Rep subunit of the cis dimer: E + ATP <==> E-ATP <==> E'-ATP <==> E'-ADP-Pi <==> E-ADP-Pi <==> E-ADP + Pi <==> E + ADP + Pi, with K1 = (2.0 +/- 0.85) x 10(5) M(-1), k2 = 22 +/- 3.5 s(-1), k(-2) < 0.12 s(-1), K3 = 4.0 +/- 0.4 (k3 > 200 s(-1)), k4 = 1.2 +/- 0.14 s(-1), k(-4) << 1.2 s(-1), K5 = 1.0 +/- 0.2 mM, and K6 = 80 +/- 8 microM. A salient feature of this mechanism is the presence of a kinetically trapped long-lived tight nucleotide binding state, E'-ADP-Pi. In the context of our "subunit switching" model for Rep dimer translocation during processive DNA unwinding [Bjornson, K. B., Wong, I., & Lohman, T. M. (1996) J. Mol. Biol. 263, 411-422], this state may serve an energy storage function, allowing the energy from the binding and hydrolysis of ATP to be harnessed and held in reserve for DNA unwinding.

ATP hydrolysis stimulates binding and release of single stranded DNA from alternating subunits of the dimeric E. coli Rep helicase: implications for ATP-driven helicase translocation

DNA helicases are motor proteins that unwind duplex DNA during DNA replication, recombination and repair in reactions that are coupled to ATP binding and hydrolysis. In the process of unwinding duplex DNA processively, DNA helicases must also translocate along the DNA filament. To probe the mechanism of ATP-driven translocation by the dimeric E. coli Rep helicase along single stranded (ss) DNA, we examined the effects of ATP on the dissociation kinetics of ssDNA from the Rep dimer. Stopped-flow experiments show that the dissociation rate of a fluorescent ss oligodeoxynucleotide bound to one subunit of the dimeric Rep helicase is stimulated by ssDNA binding to the other subunit, and that the rate of this ssDNA exchange reaction is further stimulated approximately 60-fold upon ATP hydrolysis. This ssDNA exchange process occurs via an intermediate in which ssDNA is transiently bound to both subunits of the Rep dimer. These results suggest a rolling or subunit switching mechanism for processive ATP-driven translocation of the dimeric Rep helicase along ssDNA. Such a mechanism requires the extreme negative cooperativity for DNA binding to the second subunit of the Rep dimer, which insures that the doubly DNA-ligated Rep (P2S2) dimer is formed only transiently and relaxes back to the singly ligated Rep (P2S) dimer. The fact that other oligomeric DNA helicases share many functional features with the dimeric Rep helicase suggests that similar mechanisms for translocation and DNA unwinding may apply to other dimeric as well as hexameric DNA helicases.

ATPase activity of Escherichia coli Rep helicase crosslinked to single-stranded DNA: implications for ATP driven helicase translocation

To examine the coupling of ATP hydrolysis to helicase translocation along DNA, we have purified and characterized complexes of the Escherichia coli Rep protein, a dimeric DNA helicase, covalently crosslinked to a single-stranded hexadecameric oligodeoxynucleotide (S). Crosslinked Rep monomers (PS) as well as singly ligated (P2S) and doubly ligated (P2S2) Rep dimers were characterized. The equilibrium and kinetic constants for Rep dimerization as well as the steady-state ATPase activities of both PS and P2S crosslinked complexes were identical to the values determined for un-crosslinked Rep complexes formed with dT16. Therefore, ATP hydrolysis by both PS and P2S complexes are not coupled to DNA dissociation. This also rules out a strictly unidirectional sliding mechanism for ATP-driven translocation along single-stranded DNA by either PS or the P2S dimer. However, ATP hydrolysis by the doubly ligated P2S2 Rep dimer is coupled to single-stranded DNA dissociation from one subunit of the dimer, although loosely (low efficiency). These results suggest that ATP hydrolysis can drive translocation of the dimeric Rep helicase along DNA by a "rolling" mechanism where the two DNA binding sites of the dimer alternately bind and release DNA. Such a mechanism is biologically important when one subunit binds duplex DNA, followed by subsequent unwinding.

ATPase activity of Escherichia coli Rep helicase is dramatically dependent on DNA ligation and protein oligomeric states

The Escherichia coli Rep helicase catalyzes the unwinding of duplex DNA using the energy derived from ATP binding and hydrolysis. Rep functions as a dimer but assembles to its active dimeric form only on binding DNA. Each promoter of a dimer contains a DNA binding site that can bind either single-stranded (S) or duplex (D) DNA. The dimer can bind up to two oligodeoxynucleotides in five DNA-ligation states: two half-ligated states, P2S and P2D, and three fully-ligated states, P2S2, P2D2, and P2SD. We have previously shown that the relative stabilities of these ligation states are allosterically regulated by the binding and hydrolysis of ATP and have proposed an "active rolling" model for DNA unwinding where the enzyme cycles through a series of these ligation states in a process that is coupled to the catalytic cycle of ATP hydrolysis [Wong, I., & Lohman, T.M., (1992), Science 256, 350-355]. THe basal ATPase activity of Rep protein is stimulated by ss DNA binding and by protein dimerization. We have measured the steady-state ATPase activities of Rep bound to dT(pT)15 in each distinct ss DNA ligation state (PS, P2S, and P2S2) to compare with our previous measurements with unligated Rep monomer (P) [Moore, K.J.M., & Lohman, T.M. (1994) Biochemistry 33, 14550]. We find the ATPase activity of Rep is influenced dramatically by both dimerization and ss DNA ligation state, with the following kcat values for ATP hydrolysis increasing by over 4 orders of magnitude: 2.1 x 10(-3) s(-1) for P, 2.17 +/- 0.04 s(-1) for PS, 16.5 +/- 0.2 s(-1) for P2S, and 71 +/- 2.5 s(-1) for P2S2 (20 mM Tris-HCl, pH 7.5, 6mM NaCl, 5 mM MgCl2, 10% glycerol, 4 degrees C). The apparent KM's for ATP hydrolysis are 2.05 +/- 0.1 microM for PS and 2.7 +/- 0.2 microM for P2S. These widely different ATPase activities reflect the allosteric effects of DNA ligation and demonstrate that cooperative communication occurs between the ATP and DNA site of both subunits of the Rep dimer. These results further emphasize the need to explicitly consider the population distribution of oligomerization and DNA ligation states of the helicase when attempting to infer information about elementary processes such as helicase translocation based solely on macroscopic steady-state ATPase measurements.

Changing the differentiation program of hematopoietic cells: retinoic acid-induced shift of eosinophil-committed cells to neutrophils

The mechanisms by which hematopoietic progenitor cells become lineage-committed remain poorly understood. A cloned subline of the AML14 cell line (AML14.3D10) that spontaneously differentiates to eosinophilic myelocytes in the absence of cytokine stimulation was obtained by limiting dilution. This subline exhibits augmented expression of interleukin-5 (IL-5) receptor alpha subunit mRNA and synthesizes all major eosinophil granule proteins. Exposure of this cell line to all-trans retinoic acid (ATRA) causes loss of eosinophilic granules and fast green staining within 48 hours, without cell death. In addition, mRNA for the IL-5 receptor alpha subunit becomes undetectable by 48 hours and the cells lose responsiveness to IL-5. Major basic protein, measured as a marker of eosinophilic granule content, decreases from more than 16 pg/cell to undetectable levels by 5 days after ATRA. Concomitant with the loss of major basic protein and fast green staining, surface expression of CD16 becomes detectable and is maximum by 10 days after ATRA. mRNA for the granulocyte colony-stimulating factor (G-CSF) receptor becomes detectable by day 5, and the cells become responsive to G-CSF. At this time, the cells appear morphologically as mature neutrophils and can reduce nitroblue tetrazolium. With continued culture, the neutrophilic cells die and the culture becomes repopulated with eosinophilic myelocytes. These findings show that it is possible to change the differentiation program of hematopoietic cells even after they show evidence of advanced lineage commitment. The AML14.3D10 subclone of AML14 will be a valuable model for study of the transcriptional regulation of the eosinophil and neutrophil differentiation programs and lineage-specific gene expression.

Haemolytic Escherichia coli strains isolated from stools of healthy cats produce cytotoxic necrotizing factor type 1 (CNF1)

A total of 159 Escherichia coli colonies isolated from the stools of 23 healthy cats were studied for production of alpha-haemolysin (Hly), enterohaemolysin (EntHly), cytotoxic necrotizing factors (CNF1 and CNF2), verotoxins (VT) and heat-labile enterotoxin (LT). Hly+CNF1+, Hly+CNF2+, Hly+VT+ and Hly+ E. coli colonies were isolated from 12 (48%), 1 (4%), 1 (4%) and 2 (8%) respectively of the cats sampled. None of the 159 E. coli colonies produced LT or EntHly. Nine of 12 Hly+CNF1+ strains from the cats belonged to serogroup O6 and eleven to serotypes (O4:K?:H5 or H-, O6:K13:H1, O6:K53:H-, O6:K53:H1, O6:K53:H7 and O6:K14:H31) found among Hly+CNF1+ E. coli that cause urinary tract infections and sepsis in humans. Furthermore, 10 Hly+CNF1+ strains from the cats expressed the mannose-resistant haemagglutination (MRHA) type III. By contrast, the majority of nontoxigenic E. coli strains were MRHA negative and belonged to different O groups. We conclude that cats are a important reservoir of Hly+CNF1+ E. coli strains that possess similar characteristics to strains that can cause extraintestinal infections in humans and that Hly+ E. coli from cats usually do not produce shiga-like toxins with cytotoxic activity on Vero cells.

Heterodimer formation between Escherichia coli Rep and UvrD proteins

DNA helicases catalyze the essential process of unwinding duplex DNA to form the single-stranded DNA intermediates required for DNA metabolic processes including replication, recombination, and repair. Most cells, possibly all, encode multiple helicases that function selectively in different processes, although some helicases can complement each other in vivo. Thus, although Escherichia coli can survive mutations or deletions of either the uvrD gene (encoding Helicase II) or the rep gene (encoding Rep helicase) separately, deletion of both rep and uvrD genes is lethal (Washburn, B. K., and Kushner, S. R. (1991) J. Bacteriol. 173,2569-2575). The Rep and UvrD polypeptides share approximately 40% sequence homology, and we have previously shown that both form homodimeric species and that the Rep homodimer appears to be the functionally active helicase. We report here that these two proteins can also interact in vitro to form a heterodimer. The heterodimer appears to be energetically more stable than the Rep homodimer but less stable than the UvrD homodimer under our conditions. The observation of Rep/UvrD heterodimer formation in vitro opens up the intriguing possibility that the heterodimer may play a physiologically important role that is distinct from the role of the Rep or UvrD homodimers. Therefore, considerations of the role of either protein in DNA metabolic processes, such as replication and repair, must include a potential role for a Rep/UvrD heterodimer.