Diagnostic and societal impact of implementing the syncope guidelines of the European Society of Cardiology (SYNERGY study).

BACKGROUND: Syncope management is fraught with unnecessary tests and frequent failure to establish a diagnosis. We evaluated the potential of implementing the 2018 European Society of Cardiology (ESC) Syncope Guidelines regarding diagnostic yield, accuracy and costs. METHODS: A multicentre pre-post study in five Dutch hospitals comparing two groups of syncope patients visiting the emergency department: one before intervention (usual care; from March 2017 to February 2019) and one afterwards (from October 2017 to September 2019). The intervention consisted of the simultaneous implementation of the ESC Syncope Guidelines with quick referral routes to a syncope unit when indicated. The primary objective was to compare diagnostic accuracy using logistic regression analysis accounting for the study site. Secondary outcome measures included diagnostic yield, syncope-related healthcare and societal costs. One-year follow-up data were used to define a gold standard reference diagnosis by applying ESC criteria or, if not possible, evaluation by an expert committee. We determined the accuracy by comparing the treating physician's diagnosis with the reference diagnosis. RESULTS: We included 521 patients (usual care, n = 275; syncope guidelines intervention, n = 246). The syncope guidelines intervention resulted in a higher diagnostic accuracy in the syncope guidelines group than in the usual care group (86% vs.69%; risk ratio 1.15; 95% CI 1.07 to 1.23) and a higher diagnostic yield (89% vs. 76%, 95% CI of the difference 6 to 19%). Syncope-related healthcare costs did not differ between the groups, yet the syncope guideline implementation resulted in lower total syncope-related societal costs compared to usual care (saving €908 per patient; 95% CI €34 to €1782). CONCLUSIONS: ESC Syncope Guidelines implementation in the emergency department with quick referral routes to a syncope unit improved diagnostic yield and accuracy and lowered societal costs. TRIAL REGISTRATION: Netherlands Trial Register, NTR6268.

Providing care for older adults in the Emergency Department: expert clinical recommendations from the European Task Force on Geriatric Emergency Medicine.

PURPOSE: Despite the rapidly expanding knowledge in the field of Geriatric Emergency Medicine in Europe, widespread implementation of change is still lacking. Many opportunities in everyday clinical care are missed to improve care for this susceptible and growing patient group. The aim was to develop expert clinical recommendations on Geriatric Emergency Medicine to be disseminated across Europe. METHODS: A group of multi-disciplinary experts in the field of Geriatric Emergency Medicine in Europe was assembled. Using a modified Delphi procedure, a prioritized list of topics related to Geriatric Emergency Medicine was created. Next, a multi-disciplinary group of nurses, geriatricians and emergency physicians performed a review of recent guidelines and literature to create recommendations. These recommendations were voted upon by a group of experts and placed on visually attractive posters. The expert group identified the following eight subject areas to develop expert recommendations on: Comprehensive Geriatric Assessment in the Emergency Department (ED), age/frailty adjusted risk stratification, delirium and cognitive impairment, medication reviews in the ED for older adults, family involvement, ED environment, silver trauma, end of life care in the acute setting. RESULTS: Eight posters with expert clinical recommendations on the most important topics in Geriatric Emergency Medicine are now available through https://posters.geriemeurope.eu/ . CONCLUSION: Expert clinical recommendations for Geriatric Emergency Medicine may help to improve care for older patients in the Emergency Department and are ready for dissemination across Europe.

Geriatric characteristics and the risk of drug-related hospital admissions in older Emergency Department patients.

PURPOSE: Drug-Related Admissions (DRAs) are a well-known problem among older patients in the Emergency Department (ED). The aim of this study was (a) to investigate the prevalence and clinical manifestations of DRAs and the responsible drugs, (b) to study the association between geriatric characteristics and DRAs, and (c) to study the predictive performance of geriatric screeners for identifying DRAs in older ED patients. METHODS: Patients aged ≥ 70 hospitalized from the ED were included. Demographics, geriatric characteristics and medications were collected. The the Acutely Presenting Older Patient (APOP)-screener, the Identification of Seniors At Risk (ISAR) and the ISAR-Hospitalized Patients (ISAR-HP) were used as geriatric screeners. Potential DRAs were identified retrospectively, the association between geriatric screeners and DRAs was investigated with logistic regression and the predictive performance was assessed by calculating the Area under the Curve (AUC) of the Receiver Operator Characteristics (ROC). RESULTS: The mean age of patients was 78 (IQR 73-83), using an average of 6 medications. Out of 240 admissions, 77 (30%) were classified as a DRA. Independent risk factors for DRAs were polypharmacy (OR 2.42; 95% CI 1.23-4.74) and the ADL dependency (OR 1.23; 95%CI 1.05-1.44). ISAR (OR 3.27; 95%CI 1.60-6.69) and ISAR-HP (OR 1.83; 95% CI 1.02-3.27) associated with increased risk of DRAs, whereas the APOP screener did not (OR 1.56; 95% CI 0.82-2.97). The predictive performance of all geriatric screeners for predicting DRAs was poor (AUC for all screeners < 0.60). CONCLUSION: DRAs are highly prevalent in older ED patients. Polypharmacy, ADL dependency and a high ISAR or ISAR-HP are associated with higher risk for DRAs, but the predictive value of geriatric screeners is insufficient.

Mortality risk for different presenting complaints amongst older patients assessed with the Manchester triage system.

PURPOSE: Older people often present to the Emergency Department with nonspecific complaints. We aimed (1) to examine characteristics of older patients presenting to the ED triaged with the presentational flowchart 'unwell adult' of the Manchester triage system (MTS) and (2) to assess the different mortality and admission rates among triage categories. METHODS: Retrospective cohort study including all consecutive patients aged 70 years and older who visited the ED of a tertiary care hospital in the Netherlands during a 1-year period. The primary outcome was 30-day mortality. Secondary outcomes were 7-day mortality, hospital admission and ED length of stay. RESULTS: 4255 patients were included in this study. Mean age was 78 years (IQR 73.9-83.4) and 2098 were male (49.3%). The MTS presentational flowchart 'unwell adult' was the most commonly used flowchart (n = 815, 19.3%). After the infrequent flowchart 'major trauma' (n = 9, 13.8%), 'unwell adult' had the highest 30-day mortality (n = 88, 10.8%). When compared to all other flowcharts, patients assigned as 'unwell adult' have significantly higher 30-day mortality rates (OR 1.89 (95%CI 1.46-2.46), p = < 0.001), also when adjusted for age, gender and triage priority (OR 1.75 (95%CI 1.32-2.31), p = < 0.001). Patients from the 'unwell adult' flowchart had the highest hospital admission rate (n = 540, 66.3%), and had among the longest ED length of stay. CONCLUSIONS: Older ED patients are most commonly assigned the presentational flowchart 'unwell adult' when using the MTS. Patients in this category have the highest non-trauma mortality and highest hospital admission rates when compared to other presenting complaints.

Alchemical absolute protein-ligand binding free energies for drug design.

The recent advances in relative protein-ligand binding free energy calculations have shown the value of alchemical methods in drug discovery. Accurately assessing absolute binding free energies, although highly desired, remains a challenging endeavour, mostly limited to small model cases. Here, we demonstrate accurate first principles based absolute binding free energy estimates for 128 pharmaceutically relevant targets. We use a novel rigorous method to generate protein-ligand ensembles for the ligand in its decoupled state. Not only do the calculations deliver accurate protein-ligand binding affinity estimates, but they also provide detailed physical insight into the structural determinants of binding. We identify subtle rotamer rearrangements between apo and holo states of a protein that are crucial for binding. When compared to relative binding free energy calculations, obtaining absolute binding free energies is considerably more challenging in large part due to the need to explicitly account for the protein in its apo state. In this work we present several approaches to obtain apo state ensembles for accurate absolute ΔG calculations, thus outlining protocols for prospective application of the methods for drug discovery.

Factors facilitating and hindering the implementation of the European Society of Cardiology Syncope Guidelines at the Emergency Department: A nationwide qualitative study.

AIMS: Syncope care is often fragmented and inefficient. Structuring syncope care through implementation of guidelines and Syncope Units has been shown to improve diagnostic yield, reduce costs and improve quality of life. We implemented the European Society of Cardiology (ESC) 2018 syncope guidelines at the Emergency Departments (ED) and established Syncope Units in five Dutch hospitals. We evaluated the implementation process by identifying factors that hinder ('barriers') and facilitate ('facilitators') the implementation. METHODS AND RESULTS: We conducted, recorded and transcribed semi-structured interviews with 19 specialists and residents involved in syncope care from neurology, cardiology, internal medicine and emergency medicine. Two researchers independently classified the reported barriers and facilitators, according to the framework of qualitative research (Flottorp), which distinguished several separate fields ('levels'). Software package Atlas.ti was used for analysis. We identified 31 barriers and 22 facilitators. Most barriers occurred on the level of the individual health care professional (e.g. inexperienced residents having to work with the guideline at the ED) and the organizational context (e.g. specialists not relinquishing preceding procedures). Participants reported most facilitators at the level of innovation (e.g. structured work-flow at the ED). The multidisciplinary Syncope Unit was welcomed as useful solution to a perceived need in clinical practice. CONCLUSION: Implementing ESC syncope guidelines at the ED and establishing Syncope Units facilitated a structured multidisciplinary work-up for syncope patients. Most identified barriers related to the individual health care professional and the organizational context. Future implementation of the multidisciplinary guideline should be tailored to address these barriers.

The APOP screener and clinical outcomes in older hospitalised internal medicine patients.

BACKGROUND: Acutely hospitalised older patients with indications related to internal medicine have high risks of adverse outcomes. We investigated whether risk stratification using the Acutely Presenting Older Patient (APOP) screening tool associates with clinical outcomes in this patient group. METHODS: Patients aged ≥ 70 years who visited the Emergency Department (ED) and were acutely hospitalised for internal medicine were followed prospectively. The APOP screener assesses demographics, physical and cognitive function at ED presentation, and predicts 3-month mortality and functional decline in the older ED population. Patients with a predicted risk ≥ 45% were considered 'high risk'. Clinical outcome was hospital length of stay (LOS), and adverse outcomes were mortality and functional decline, 3 and 12 months after hospitalisation. RESULTS: We included 319 patients, with a median age of 80 (IQR 74-85) years, of whom 94 (29.5%) were categorised as 'high risk' by the APOP screener. These patients had a longer hospital LOS compared to 'low risk' patients 5 (IQR 3-10) vs. 3 (IQR 1-7) days, respectively; p = 0.006). At 3 months, adverse outcomes were more frequent in 'high risk' patients compared to 'low risk' patients (59.6% vs. 34.7%, respectively; p < 0.001). At 12 months, adverse outcomes (67.0% vs. 46.2%, respectively; p = 0.001) and mortality (48.9% vs. 28.0%, respectively; p < 0.001) were greater in 'high risk' compared to 'low risk' patients. CONCLUSION: The APOP screener identifies acutely hospitalised internal medicine patients at high risk for poor short and long-term outcomes. Early risk stratification at admission could aid in individualised treatment decisions to optimise outcomes for older patients.

Optimization of the APOP screener to predict functional decline or mortality in older emergency department patients: Cross-validation in four prospective cohorts.

INTRODUCTION: Many screening instruments to predict adverse health outcomes in older patients visiting the emergency department (ED) have been developed, but successful implementation has been hampered because they are insufficiently validated or not tailored for the intended use of everyday clinical practice. The present study aims to refine and validate an existing screening instrument (the APOP screener) to predict 90-day functional decline or mortality in older ED patients. METHODS: Consecutive older patients (≥70 years) visiting the EDs of four hospitals were included and prospectively followed. First, an expert panel used predefined criteria to decide which independent predictors (including demographics, illness severity and geriatric parameters) were suitable for refinement of the model predicting functional decline or mortality after 90 days. Second, the model was cross-validated in all four hospitals and predictive performance was assessed. Additionally, a pilot study among triage nurses experiences and clinical usability of the APOP screener was conducted. RESULTS: In total 2629 older patients were included, with a median age of 79 years (IQR 74-84). After 90 days 805 patients (30.6%) experienced functional decline or mortality. The refined prediction model included age, gender, way of arrival, need of regular help, need help in bathing/showering, hospitalization the prior six months and impaired cognition. Calibration was good and cross-validation was successful with a pooled area under the curve of 0.71 (0.69-0.73). In the top 20% patients predicted to be at highest risk in total 58% (95%CI 54%-62%) experienced functional decline or mortality. Triage nurses found the screener well suited for clinical use, with room for improvement. CONCLUSION: In conclusion, optimization of the APOP screener resulted in a short and more simplified screener, which adequately identifies older ED patients at highest risk for functional decline or mortality. The findings of the pilot study were promising for clinical use.

Impaired cognition is associated with adverse outcome in older patients in the Emergency Department; the Acutely Presenting Older Patients (APOP) study.

Objective: to investigate whether cognitive impairment, measured early after Emergency Department (ED) arrival and irrespective of its cause, is independently associated with functional decline or mortality after 3 and 12 months in older ED patients. Design and setting: a prospective multi-centre cohort study in all Acutely Presenting Older Patients visiting the Emergency Department (APOP study) of three hospitals in the Netherlands. Participants: 2,130 patients, ≥70 years. Measurements: data on demographics, disease severity and geriatric characteristics were collected during the first hour of the ED visit. Cognition was measured using the 6-Item-Cognitive-Impairment-Test ('6CIT'). Cognitive impairment was defined as 6CIT ≥11, self-reported dementia or the inability to perform the cognition test. The composite adverse outcome after 3 and 12 months was defined as a 1-point decrease in Katz Activities of Daily Living (ADL), new institutionalisation or mortality. Multivariable regression analysis was used to assess whether cognitive impairment independently associates with adverse outcome. Results: of 2,130 included patients, 588 (27.6%) had cognitive impairment at baseline and 654 patients (30.7%) suffered from adverse outcome after 3 months. Cognitive impairment associated with increased risk for adverse outcome (adjusted odds ratio (OR) 1.72, 95%CI 1.37-2.17). After 12 months, 787 patients (36.9%) suffered from adverse outcome. Again, cognitive impairment independently associated with increased risk for adverse outcome (adjusted OR 1.89, 95%CI 1.46-2.46). ORs were similar for patients who were discharged home versus hospitalised patients. Conclusion: cognitive impairment measured during the early stages of ED visit, irrespective of the cause, is independently associated with adverse outcome after 3 and 12 months in older patients.

Optimising the ISAR-HP to screen efficiently for functional decline in older patients.

INTRODUCTION: The Identification of Seniors At Risk-Hospitalised Patients (ISAR-HP) has recently been included in guidelines as a frailty indicator to identify patients for comprehensive geriatric assessment. Previous studies showed that the conventional cut-off score incorrectly classifies a high percentage of patients as high risk. We aimed to optimise the predictive value of ISAR-HP by using different cut-offs in older acutely hospitalised patients. METHODS: A prospective follow-up study was performed in two Dutch hospitals. Acutely hospitalised patients aged ≥ 70 years were included. Demographics, illness severity parameters, geriatric measurements and the ISAR-HP scores were obtained at baseline. The primary outcome was a combined end point of functional decline or mortality during 90-day follow-up. RESULTS: In total 765 acutely hospitalised older patients were included, with a median age of 79 years, of whom 276 (36.1%) experienced functional decline or mortality. The conventional ISAR-HP cut-off of ≥ 2 assigned 432/765 patients (56.5%) as high risk, with a positive predictive value (PPV) of 0.49 (95%CI 0.45-0.54) and a negative predictive value of 0.81 (95%CI 0.76-0.85). Thus, 51% of those whom the ISAR-HP denoted as high risk did not experience the outcome of interest. Raising the cut-off to ≥ 4 assigned 205/765 patients (26.8%) as high risk, with a marginally increased PPV to 0.55 (95%CI 0.48-0.62). CONCLUSION: The ISAR-HP with the conventional cut-off of ≥ 2 incorrectly identifies a large group of patients at high risk for functional decline or mortality and raising the cut-off to 4 only marginally improved performance. Caution is warranted to ensure efficient screening and follow-up interventions.

Predicting adverse health outcomes in older emergency department patients: the APOP study.

BACKGROUND: Older patients experience high rates of adverse outcomes after an emergency department (ED) visit. Early identification of those at high risk could guide preventive interventions and tailored treatment decisions, but available models perform poorly in discriminating those at highest risk. The present study aims to develop and validate a prediction model for functional decline and mortality in older patients presenting to the ED. METHODS: A prospective follow-up study in patients aged ≥ 70, attending the EDs of the LUMC, the Netherlands (derivation) and Alrijne Hospital, the Netherlands (validation) was conducted. A baseline assessment was performed and the main outcome, a composite of functional decline and mortality, was obtained after 90 days of follow-up. RESULTS: In total 751 patients were enrolled in the Leiden University Medical Center of whom 230 patients (30.6%) experienced the composite outcome and 71 patients (9.5%) died. The final model for the composite outcome resulted in an area under the curve (AUC) of 0.73 (95% CI 0.67-0.77) and was experienced in 69% of the patients at highest risk. For mortality the AUC was 0.79 (95% CI 0.73-0.85) and 36% of the patients at highest risk died. External validation in 881 patients of Alrijne Hospital showed an AUC of 0.71 (95% CI 0.67-0.75) for the composite outcome and 0.67 (95% CI 0.60-0.73) for mortality. CONCLUSION: We successfully developed and validated prediction models for 90-day composite outcome and 90-day mortality in older emergency patients. The benefits for patient management by implementing these models with preventive interventions have to be investigated.

The anti-protozoal drug pentamidine blocks KIR2.x-mediated inward rectifier current by entering the cytoplasmic pore region of the channel.

BACKGROUND AND PURPOSE: Pentamidine is a drug used in treatment of protozoal infections. Pentamidine treatment may cause sudden cardiac death by provoking cardiac arrhythmias associated with QTc prolongation and U-wave alterations. This proarrhythmic effect was linked to inhibition of hERG trafficking, but not to acute block of ion channels contributing to the action potential. Because the U-wave has been linked to the cardiac inward rectifier current (I(K1)), we examined the action and mechanism of pentamidine-mediated I(K1) block. EXPERIMENTAL APPROACH: Patch clamp measurements of I(K1) were made on cultured adult canine ventricular cardiomyocytes, K(IR)2.1-HEK293 cells and K(IR)2.x inside-out patches. Pentamidine binding to cytoplasmic amino acid residues of K(IR)2.1 channels was studied by molecular modelling. KEY RESULTS: Pentamidine application (24 h) decreased I(K1) in cultured canine cardiomyocytes and K(IR)2.1-HEK293 cells under whole cell clamp conditions. Pentamidine inhibited I(K1) in K(IR)2.1-HEK293 cells 10 min after application. When applied to the cytoplasmic side under inside-out patch clamp conditions, pentamidine block of I(K1) was acute (IC(50)= 0.17 microM). Molecular modelling predicted pentamidine-channel interactions in the cytoplasmic pore region of K(IR)2.1 at amino acids E224, D259 and E299. Mutation of these conserved residues to alanine reduced pentamidine block of I(K1). Block was independent of the presence of spermine. K(IR)2.2, and K(IR)2.3 based I(K1) was also sensitive to pentamidine blockade. CONCLUSIONS AND IMPLICATIONS: Pentamidine inhibits cardiac I(K1) by interacting with three negatively charged amino acids in the cytoplasmic pore region. Our findings may provide new insights for development of specific I(K1) blocking compounds.

A plate reader-based method for cell water permeability measurement.

Cell volume and water permeability measurements in cultured mammalian cells are typically conducted under a light microscope. Many of the employed approaches are time consuming and not applicable to a study of confluent epithelial cell monolayers. We present here an adaptation of a calcein-quenching-based approach for a plate reader. A standard curve of fluorescence intensities at equilibrium has been recorded, following a shift from 285 mosmol/kgH(2)O to a series of altered extracellular osmolyte concentrations, ranging from final concentrations of 185 to 585 mosmol/kgH(2)O, by changing buffer d-mannitol concentrations. Similarly, according average cell volumes have been measured in suspension in a Coulter counter (particle-sizing device). Based on these measurements, we have derived an equation that facilitates the modeling of cell volume changes based on fluorescence intensity changes. We have utilized the method to study the role of a carboxyl-terminus aquaporin (AQP)-2 phosphorylation site, which is known to affect AQP2 membrane trafficking, in heterologous type I Madin-Darby canine kidney cells. We find that water permeability in cells expressing phosphorylation site mutants was in the following order: AQP2-S256D > AQP2 wild-type > AQP2-S256A. We propose that the method can be applied to study AQP function and more generally to study cell volume changes in adherent cell lines. Furthermore, it should be adaptable for AQP inhibitor screening in chemical compound libraries.

High sensitivity imaging Thomson scattering for low temperature plasma.

A highly sensitive imaging Thomson scattering system was developed for low temperature (0.1-10 eV) plasma applications at the Pilot-PSI linear plasma generator. The essential parts of the diagnostic are a neodymium doped yttrium aluminum garnet laser operating at the second harmonic (532 nm), a laser beam line with a unique stray light suppression system and a detection branch consisting of a Littrow spectrometer equipped with an efficient detector based on a "Generation III" image intensifier combined with an intensified charged coupled device camera. The system is capable of measuring electron density and temperature profiles of a plasma column of 30 mm in diameter with a spatial resolution of 0.6 mm and an observational error of 3% in the electron density (n(e)) and 6% in the electron temperature (T(e)) at n(e) = 4 x 10(19) m(-3). This is achievable at an accumulated laser input energy of 11 J (from 30 laser pulses at 10 Hz repetition frequency). The stray light contribution is below 9 x 10(17) m(-3) in electron density equivalents by the application of a unique stray light suppression system. The amount of laser energy that is required for a n(e) and T(e) measurement is 7 x 10(20)n(e) J, which means that single shot measurements are possible for n(e)>2 x 10(21) m(-3).

The 5A structure of heterologously expressed plant aquaporin SoPIP2;1.

SoPIP2;1 is one of the major integral proteins in spinach leaf plasma membranes. In the Xenopus oocyte expression system its water channel activity is regulated by phosphorylation at the C terminus and in the first cytosolic loop. To assess its structure, SoPIP2;1 was heterologously expressed in Pichia pastoris as a His-tagged protein and in the non-tagged form. Both forms were reconstituted into 2D crystals in the presence of lipids. Tubular crystals and double-layered crystalline sheets of non-tagged SoPIP2;1 were observed and analyzed by cryo-electron microscopy. Crystalline sheets were highly ordered and diffracted electrons to a resolution of 2.96A. High-resolution projection maps of tilted specimens provided a 3D structure at 5A resolution. Superposition of the SoPIP2;1 potential map with the atomic model of AQP1 demonstrates the generally well conserved overall structure of water channels. Differences concerning the extracellular loop A explain the particular crystal contacts between oppositely oriented membrane sheets of SoPIP2;1 2D crystals, and may have a function in rapid volume changes observed in stomatal guard cells or mesophyll protoplasts. This crystal packing arrangement provides access to the phosphorylated C terminus as well as the loop B phosphorylation site for studies of channel gating.

Progress in the analysis of membrane protein structure and function.

Structural information on membrane proteins is sparse, yet they represent an important class of proteins that is encoded by about 30% of all genes. Progress has primarily been achieved with bacterial proteins, but efforts to solve the structure of eukaryotic membrane proteins are also increasing. Most of the structures currently available have been obtained by exploiting the power of X-ray crystallography. Recent results, however, have demonstrated the accuracy of electron crystallography and the imaging power of the atomic force microscope. These instruments allow membrane proteins to be studied while embedded in the bi-layer, and thus in a functional state. The low signal-to-noise ratio of cryo-electron microscopy is overcome by crystallizing membrane proteins in a two-dimensional protein-lipid membrane, allowing its atomic structure to be determined. In contrast, the high signal-to-noise ratio of atomic force microscopy allows individual protein surfaces to be imaged at sub-nanometer resolution, and their conformational states to be sampled. This review summarizes the steps in membrane protein structure determination and illuminates recent progress.

Water permeation across biological membranes: mechanism and dynamics of aquaporin-1 and GlpF.

"Real time" molecular dynamics simulations of water permeation through human aquaporin-1 (AQP1) and the bacterial glycerol facilitator GlpF are presented. We obtained time-resolved, atomic-resolution models of the permeation mechanism across these highly selective membrane channels. Both proteins act as two-stage filters: Conserved fingerprint [asparagine-proline-alanine (NPA)] motifs form a selectivity-determining region; a second (aromatic/arginine) region is proposed to function as a proton filter. Hydrophobic regions near the NPA motifs are rate-limiting water barriers. In AQP1, a fine-tuned water dipole rotation during passage is essential for water selectivity. In GlpF, a glycerol-mediated "induced fit" gating motion is proposed to generate selectivity for glycerol over water.

A refined structure of human aquaporin-1.

A refined structure of the human water channel aquaporin-1 is presented. The model rests on the high resolution X-ray structure of the homologous bacterial glycerol transporter GlpF, electron crystallographic data at 3.8 A resolution and a multiple sequence alignment of the aquaporin superfamily. The crystallographic R and free R values (36.7% and 37.8%) for the refined structure are significantly lower than for previous models. Improved geometry and enhanced stability in molecular dynamics simulations demonstrate a significant improvement of the aquaporin-1 structure. Comparison with previous aquaporin-1 models shows significant differences, not only in the loop regions, but also in the core of the water channel.

Essential dynamics of reversible peptide folding: memory-free conformational dynamics governed by internal hydrogen bonds.

A principal component analysis has been applied on equilibrium simulations of a beta-heptapeptide that shows reversible folding in a methanol solution. The analysis shows that the configurational space contains only three dense sub-states. These states of relatively low free energy correspond to the "native" left-handed helix, a partly helical intermediate, and a hairpin-like structure. The collection of unfolded conformations form a relatively diffuse cloud with little substructure. Internal hydrogen-bonding energies were found to correlate well with the degree of folding. The native helical structure folds from the N terminus; the transition from the major folding intermediate to the native helical structure involves the formation of the two most C-terminal backbone hydrogen bonds. A four-state Markov model was found to describe transition frequencies between the conformational states within error limits, indicating that memory-effects are negligible beyond the nanosecond time-scale. The dominant native state fluctuations were found to be very similar to unfolding motions, suggesting that unfolding pathways can be inferred from fluctuations in the native state. The low-dimensional essential subspace, describing 69% of the collective atomic fluctuations, was found to converge at time-scales of the order of one nanosecond at all temperatures investigated, whereas folding/unfolding takes place at significantly longer time-scales, even above the melting temperature.