Aggregative adherence fimbriae form compact structures as seen by SAXS

Bacterial colonization is mediated by fimbriae, which are thin hair-like appendages dispersed from the bacterial surface. The aggregative adherence fimbriae from enteroaggregative E. coli are secreted through the outer membrane and consist of polymerized minor and major pilin subunits. Currently, the understanding of the structural morphology and the role of the minor pilin subunit in the polymerized fimbriae are limited. In this study we use small-angle X-ray scattering to reveal the structural morphology of purified fimbriae in solution. We show that the aggregative fimbriae are compact arrangements of subunit proteins Agg5A + Agg3B which are assembled pairwise on a flexible string rather than extended in relatively straight filaments. Absence of the minor subunit leads to less compact fimbriae, but did not affect the length. The study provides novel insights into the structural morphology and assembly of the aggregative adherence fimbriae. Our study suggests that the minor subunit is not located at the tip of the fimbriae as previously speculated but has a higher importance for the assembled fimbriae by affecting the global structure.

Multi-Step Unfolding and Rearrangement of α-Lactalbumin by SDS Revealed by Stopped-Flow SAXS

Interactions between proteins and surfactants are both of fundamental interest and relevant for applications in food, cosmetics and detergency. The anionic surfactant sodium dodecyl sulfate (SDS) denatures essentially all proteins. Denaturation typically involves a number of distinct steps where growing numbers of SDS molecules bind to the protein, as seen in multidisciplinary approaches combining several complementary techniques. We adopt this approach to study the SDS-induced unfolding of Ca2+-depleted α-lactalbumin (aLA), a protein particularly sensitive toward denaturation by surfactants. By combining stopped-flow mixing of protein and surfactant solutions with stopped-flow synchrotron small-angle X-ray scattering (SAXS), circular dichroism (CD) and Trp fluorescence, together with information from previous calorimetric studies, we construct a detailed picture of the unfolding process at the level of both protein and surfactant. A protein-surfactant complex is formed within the dead time of mixing (2.5 ms). Initially a cluster of SDS molecules binds asymmetrically, i.e., to one side of the protein, after which aLA redistributes around the SDS cluster. This occurs in two kinetic steps where the complex grows in number of both SDS and protein molecules, concomitant with protein unfolding. During these steps, the core-shell complex undergoes changes in shell thickness as well as core shape and radius. The entire process is very sensitive to SDS concentration and completes within 10 s at an SDS:aLA ratio of 9, decreasing to 0.2 s at 60 SDS:aLA. The number of aLA molecules per SDS complex drops from 1.9 to 1.0 over this range of ratios. While both CD and Trp kinetics reveal a fast and a slow conformational transition, only the slow transition is observed by SAXS, indicating that the protein-SDS complex (which is monitored by SAXS) adjusts to the presence of the unfolded protein. We attribute the rapid unfolding of aLA to its predominantly α-helical structure, which persists in SDS (albeit as isolated helices), enabling aLA to unfold without undergoing major secondary structural changes unlike β-sheet rich proteins. Nevertheless, the overall unfolding steps are broadly similar to those of the more β-rich protein β-lactoglobulin, suggesting that this unfolding model is representative of the general process of SDS-unfolding of proteins.

Effects of multiple scattering encountered for various small-angle scattering model functions

The means by which multiple scattering contributions in experimental small-angle scattering data can be estimated, and how they can be included in the data analysis, are reviewed and discussed. The multiple scattering effects for a range of relevant model scattering functions are calculated using semi-analytically derived solutions to Hankel transforms as well as Monte Carlo simulations.

In small-angle scattering theory and data modeling, it is generally assumed that each scattered ray – photon or neutron – is only scattered once on its path through the sample. This assumption greatly simplifies the interpretation of the data and is valid in many cases. However, it breaks down under conditions of high scattering power, increasing with sample concentration, scattering contrast, sample path length and ray wavelength. For samples with a significant scattering power, disregarding multiple scattering effects can lead to erroneous conclusions on the structure of the investigated sample. In this paper, the impact of multiple scattering effects on different types of scattering pattern are determined, and methods for assessing and addressing them are discussed, including the general implementation of multiple scattering effects in structural model fits. The modification of scattering patterns by multiple scattering is determined for the sphere scattering function and the Gaussian function, as well as for different Sabine-type functions, including the Debye–Andersen–Brumberger (DAB) model and the Lorentzian scattering function. The calculations are performed using the semi-analytical convolution method developed by Schelten & Schmatz [J. Appl. Cryst. (1980 ▸). 13, 385–390], facilitated by analytical expressions for intermediate functions, and checked with Monte Carlo simulations. The results show how a difference in the shape of the scattering function plotted versus momentum transfer q results in different multiple scattering effects at low q, where information on the particle mass and radius of gyration is contained.

Aquaporin-Based Biomimetic Polymeric Membranes: Approaches and Challenges

In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes.

High electrokinetic energy conversion efficiency in charged nanoporous nitrocellulose/sulfonated polystyrene membranes

The synthesis, characterization, and electrokinetic energy conversion performance have been investigated experimentally in a charged polymeric membrane based on a blend of nitrocellulose and sulfonated polystyrene. The membrane is characterized by a moderate ion exchange capacity and a relatively porous structure with average pore diameter of 11 nm. With electrokinetic energy conversion, pressure can be converted directly into electric energy and vice versa. From the electrokinetic transport properties, a remarkably large intrinsic maximum efficiency of 46% is found. It is anticipated that the results are an experimental verification of theoretical models that predict high electrokinetic energy conversion efficiency in pores with high permselectivity and hydrodynamic slip flow. Furthermore, the result is a promising step for obtaining efficient low-cost electrokinetic generators and pumps for small or microscale applications.

Selecting analytical tools for characterization of polymersomes in aqueous solution

We present 17 techniques to analyze polymersomes, in terms of their size, bilayer properties, elastic properties or surface charge.

Monitoring the transition from spherical to polymer-like surfactant micelles using small-angle X-ray scattering

Despite over a century of modern surfactant science, the kinetic pathways of morphological transitions in micellar systems are still not well understood. This is mainly as a result of the lack of sufficiently fast methods that can capture the structural changes of such transitions. Herein, a simple surfactant system consisting of sodium dodecyl sulfate (SDS) in aqueous NaCl solutions is investigated. Combining synchrotron radiation small-angle X-ray scattering (SAXS) with fast stopped-flow mixing schemes allows monitoring the process where polymer-like micelles are formed from globular micelles when the salt concentration is suddenly increased. The results show that "worm-like" micelles are formed by fusion of globular micelles and short cylinders in a fashion that bears similarities to a step-like polymerization process.

Formation of dynamic soluble surfactant-induced amyloid β peptide aggregation intermediates

Intermediate amyloidogenic states along the amyloid β peptide (Aβ) aggregation pathway have been shown to be linked to neurotoxicity. To shed more light on the different structures that may arise during Aβ aggregation, we here investigate surfactant-induced Aβ aggregation. This process leads to co-aggregates featuring a β-structure motif that is characteristic for mature amyloid-like structures. Surfactants induce secondary structure in Aβ in a concentration-dependent manner, from predominantly random coil at low surfactant concentration, via β-structure to the fully formed α-helical state at high surfactant concentration. The β-rich state is the most aggregation-prone as monitored by thioflavin T fluorescence. Small angle x-ray scattering reveals initial globular structures of surfactant-Aβ co-aggregated oligomers and formation of elongated fibrils during a slow aggregation process. Alongside this slow (minutes to hours time scale) fibrillation process, much faster dynamic exchange (k(ex) ∼1100 s(-1)) takes place between free and co-aggregate-bound peptide. The two hydrophobic segments of the peptide are directly involved in the chemical exchange and interact with the hydrophobic part of the co-aggregates. Our findings suggest a model for surfactant-induced aggregation where free peptide and surfactant initially co-aggregate to dynamic globular oligomers and eventually form elongated fibrils. When interacting with β-structure promoting substances, such as surfactants, Aβ is kinetically driven toward an aggregation-prone state.

Direct observation of the formation of surfactant micelles under nonisothermal conditions by synchrotron SAXS

Self-assembly of amphiphilic molecules into micelles occurs on very short times scales of typically some milliseconds, and the structural evolution is therefore very challenging to observe experimentally. While rate constants of surfactant micelle kinetics have been accessed by spectroscopic techniques for decades, so far no experiments providing detailed information on the structural evolution of surfactant micelles during their formation process have been reported. In this work we show that by applying synchrotron small-angle X-ray scattering (SAXS) in combination with the stopped-flow mixing technique, the entire micelle formation process from single surfactants to equilibrium micelles can be followed in situ. Using a sugar-based surfactant system of dodecyl maltoside (DDM) in dimethylformamide (DMF), micelle formation can be induced simply by adding water, and this can be followed in situ by SAXS. Mixing of water and DMF is an exothermic process where the micelle formation process occurs under nonisothermal conditions with a temperature gradient relaxing from about 40 to 20 °C. A kinetic nucleation and growth mechanism model describing micelle formation by insertion/expulsion of single molecules under nonisothermal conditions was developed and shown to describe the data very well.

Composition, structure and properties of POPC-triolein mixtures. Evidence of triglyceride domains in phospholipid bilayers

We have in this study investigated the composition, structure and spectroscopical properties of multilamellar vesicles composed of a phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and up to 10mol% of triolein (TO), a triglyceride. We found in agreement with previous results that the mixtures with 10mol% TO spontaneously separate into two distinct phases, heavy (HF) and light (LF), with different densities and found this also to be the case for 2 and 5mol% TO. The compositions of the two phases were investigated by quantitative lipid mass spectrometric analysis, and with this method we found that TO had a solubility maximum of about 4mol% in the HF, whereas it was markedly up-concentrated in the LF. Electron paramagnetic resonance spectroscopy indicated POPC membranes of all tested concentrations of TO in both phases to be almost unperturbed by the presence of TO and to exist as vesicular structures containing entrapped water. Bilayer structure of the membranes was supported by small angle X-ray scattering that showed the membranes to form a lamellar phase. Fluorescence spectroscopy with the polarity sensitive dye Nile red revealed, that the LF samples with more than 5mol% TO contained pure TO domains. These observations are consistent with an earlier MD simulation study by us and our co-workers suggesting triglycerides to be located in lens shaped, blister-like domains between the two lipid bilayer leaflets (Khandelia et al. (2010) [26]).

Structure of PEP–PEO block copolymer micelles: exploiting the complementarity of small-angle X-ray scattering and static light scattering

The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP–PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8–49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core–shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.

Predictors of coronary in-stent restenosis: importance of angiotensin-converting enzyme gene polymorphism and treatment with angiotensin-converting enzyme inhibitors

OBJECTIVES

This study aimed to clarify the role of the angiotensin-converting enzyme (ACE) gene polymorphism in the development of in-stent restenosis.

BACKGROUND

In-stent restenosis occurs after treatment of coronary artery stenosis in 12% to 32% of coronary interventions with stents. Experimental and clinical studies have suggested that the deletion/insertion (D/I) polymorphism of the ACE gene plays a role in this.

METHODS

Quantitative coronary angiography before, immediately after and six months after stent implantation were compared in 369 patients, in whom D/I typing of the ACE gene was performed.

RESULTS

At follow-up we found no differences between the three genotypes in minimal lumen diameter (homozygotes with two deletion alleles in the ACE gene [DD], 2.20 mm; heterozygotes with one deletion and one insertion allele in the ACE gene [DI], 2.19 mm; and homozygotes with two insertion alleles in the ACE gene [II], 2.25 mm). The corresponding diameter stenoses were: DD: 25%, DI: 27%, II: 27% (p = NS), and the frequency of restenosis (>50% diameter stenosis) was: DD: 15.7%, DI: 11.0% and II: 16.4% (p = NS). Logistic regression analysis identified diabetes (odds ratio [OR]: 3.0, 95% confidence interval [CI]: 1.0 to 8.7), lesion length (OR: 1.1, 95% CI: 1.01 to 1.30) and minimal lumen diameter immediately after the intervention (OR: 0.3, 95% CI: 0.14 to 0.85) as predictors of in-stent restenosis. In a post hoc analysis of patients treated versus those not treated with an ACE-inhibitor antagonist or an angiotensin receptor antagonist, we found an increased frequency of in-stent restenosis in the DD genotypes (40% vs. 12%, p = 0.006).

CONCLUSIONS

The D/I polymorphism is not an independent predictor of coronary in-stent restenosis in general, but it may be of clinical importance in patients treated with ACE inhibitors or angiotensin receptor antagonists.

University of Iowa Hospital and Clinics: outcomes management

Delivery of quality patient care and management of patient outcomes is critical to the success of academic medical centers in the ever-changing health care market. The University of Iowa Hospitals and Clinics (UIHC) promotes quality care through the provision of organizational structures and processes that are described in this article. In addition, quality of care and outcomes management are described by members in various roles within the UIHC health care system. It is the authors' belief that understanding quality from these various perspectives helps UIHC work across departments to achieve excellence in patient care.

Accelerating impact of diabetes mellitus on mortality in the years following an acute myocardial infarction. TRACE Study Group. Trandolapril Cardiac Evaluation

AIMS

The development of risk associated with diabetes mellitus during long-term follow-up after a myocardial infarction has not been studied in detail. We have studied time-related changes of risk of death during 10 years of follow-up in a cohort of patients not treated with thrombolytic therapy (the Glostrup cohort) and during 6 years in a cohort receiving such treatment in 40% of cases (the TRACE cohort).

METHODS

A subgroup analysis of two cohorts: the Glostrup cohort, which consisted of consecutive cases of acute myocardial infarction who were admitted to one hospital between 1979 and 1983; the TRACE cohort which was comprised of patients with an acute myocardial infarction screened for entry into the Trandolapril Cardiac Evaluation study between May 1990 and June 1992. The Glostrup cohort consisted of 1954 patients and follow-up was for 10 years, The TRACE cohort consisted of 6676 patients and follow-up was for 6 years. Outcome measure was total death.

RESULTS

A diagnosis of diabetes mellitus was present in 12% of the two study populations. In multivariate analysis, diabetes mellitus had an independent adverse effect on mortality which increased with time. In the Glostrup cohort risk ratio between day 0 and day 30 was 1.17 and increased to 2.51 (P=0.0002) 7-9 years after discharge from hospital. A similar increase in the risk ratio of diabetes mellitus on mortality was observed in the TRACE cohort (risk ratio for days 0-30 was 1.03, and for years 4-6 was 1.74 (P=0.0001).

CONCLUSION

Diabetes mellitus has no independent influence on mortality immediately following an acute myocardial infarction, but has an important influence on long-term mortality which increases with time. The implication is that the effect of intervention against diabetes in patients with acute myocardial infarction and diabetes mellitus must be evaluated over a long course of time.

Improvement in long-term prognosis of elderly patients with acute myocardial infarction after the introduction of intravenous thrombolytic therapy

Survival rate from a "thrombolytic" period of 351 patients above 66 years of age with acute myocardial infarction (AMI) was compared with that of 289 patients from a "prethrombolytic" period. The two groups were comparable regarding sex, age, previous AMI, cerebrovascular events, morbidity and mortality during admission. Survival rates after four years were 45.0% in the "thrombolytic" group and 38.4% in the "prethrombolytic" group (p = 0.047, log rank test). Using the Cox proportional hazard analysis, thrombolytic therapy was shown to be an independent prognostic predictor in "the thrombolytic population" with a relative risk of death from day 30 to end of follow-up of 0.4 (95% confidence interval 0.2-0.8). No interaction was found between age and thrombolysis. Although only one-fifth of the patients with AMI were eligible for thrombolysis, this treatment may have contributed to the improved long-term survival.

Does in-hospital ventricular fibrillation affect prognosis after myocardial infarction?

AIM

The aim of this study was to estimate the prognostic information to be gained from ventricular fibrillation in patients with myocardial infarction.

METHODS AND RESULTS

We studied 4259 consecutive patients with myocardial infarction admitted to one centre in 1977-1988. Five hundred and twenty-eight (12.4%) of the patients had ventricular fibrillation in hospital. The following risk factors were included in multivariate models to estimate their importance for 30-day and long-term (median 7 year) prognosis: age, gender, ventricular fibrillation, congestive heart failure, pulmonary oedema, cardiogenic shock, other cardiac arrest and atrial fibrillation. We found that the odds ratio for death on days 6.30 was 6.34 (3.55-11.30, 95% confidence limits, P < 0.001) for patients with primary ventricular fibrillation (without heart failure) and 4.06 (2.68-6.14, P < 0.001) for patients with ventricular fibrillation secondary to heart failure compared to patients without ventricular fibrillation. For patients surviving more than 30 days, relative risk of death in those with ventricular fibrillation was 1.11 (95% confidence interval 0.93-1.34, P = 0.26). Logistic regression analysis of relative risk associated with ventricular fibrillation in time intervals, indicated that the importance of ventricular fibrillation for risk of death was exhausted during the initial 60 days after infarction.

CONCLUSION

Ventricular fibrillation is associated with an independent increased risk of death within 0-60 days after infarction. After this period, the prognosis in survivors of ventricular fibrillation does not differ significantly from patients without ventricular fibrillation.

Education of staff and students in health care settings: integrating practice and research

A cooperative program between the University of Iowa Hospitals and Clinics (UIHC) Department of Social Service (DSS) and the University of Iowa School of Social Work (UISSW) integrates faculty and students with clinicians for both practice and/or research internships. This program has endeavored to enhance practice and research social work through the development of (1) multiple student training programs offering both practice and research placement opportunities, (2) a jointly appointed faculty position between the UISSW and the UIHC DSS designed to improve researchers' access to and involvement with practice and practitioners' involvement in practice research, and (3) specialized student training programs including research projects in practice specialties. This project has helped clinicians conduct research, provided students with practical research experience within a clinical setting, and has increased the likelihood that both staff and students will participate in research.

[Adverse effects of subcutaneous administration of erythropoietin solution versus lyophilisate in patients receiving hemodialysis]

Twenty-two patients in haemodialysis were treated with erythropoietin subcutaneously in a double-blinded cross-over study with erythropoietin prepared either as a lyophilisate or an albumin-solution. The aim was to compare local reactions and pain. Both preparations were tolerated well. No major adverse reactions were seen. Erythropoietin albumin-solution was associated with significantly more burning pain than erythropoietin lyophilisate. Allergy does not seem to be involved. Albumin could be the irritative agent.

Prognosis of ventricular fibrillation in hospital

In a retrospective study of 520 patients with in-hospital ventricular fibrillation 421 (81%) had acute myocardial infarction (MI), 66 (13%) had ischaemic heart disease (IHD) without MI, 33 (6%) had no signs of IHD. The in-hospital mortality of these three groups was 51%, 52%, and 27%, respectively (P = 0.01). Logistic regression analysis demonstrated that heart failure and cardiogenic shock were significant risk factors for in-hospital death among patients with IHD. Among discharged patients 1 and 5 years survival was 78% and 51% for patients with MI, 63% and 25% for patients with IHD, 67% and 54% for patients without IHD. A proportional hazard model demonstrated old age, heart failure and cardiogenic shock as risk factors for long-term prognosis, while MI was associated with a reduced relative risk ratio = 0.58 of long-term mortality among patients with IHD. In conclusion, patients with known IHD suffering in-hospital VF without AMI have a very poor short- and long-term prognosis. These patients need extensive cardiac examination.

[Hypercalcemia during immobilization and prolonged anuria treated with disodium clodronate]

Severe hypercalcaemia was observed during prolonged anuria and prolonged immobilization in a previously healthy 34 years old male after a severe trauma caused by a traffic accident. Other causes of the hypercalcaemia were evaluated, and even though granulomas of unidentified nature were found in the liver after partial resection due to traumatic rupture the immobile state was concluded to be the major cause. A maximum calcium value of 4.44 mmol/l was seen after 10 weeks immobilization. The patient was treated with daily dialysis and, even though the calcium content in the dialysis fluid was reduced, only a minor effect was seen on the calcium level. After eight weeks of hypercalcaemia, the patient was treated with disodium clodronate intravenously 400 mg for daily five days. However, the calcium level was not normalized and the treatment was repeated with a further reduction in the calcium level. If immobilization is a major contributory factor to hypercalcaemia, disodium clodronate seems to be a safe and effective treatment.

[Prognosis in early and late ventricular fibrillation after acute myocardial infarction]

Of 413 patients with in-hospital ventricular fibrillation complicating acute myocardial infarction 281 had early (less than 48 hours post infarction) ventricular fibrillation and 132 had late ventricular fibrillation. In-hospital and longterm prognoses were not influenced by time of ventricular fibrillation, but advanced age and signs of reduced left ventricular function were found to be independent significant risk factors for short and longterm prognoses.

Prognosis of late versus early ventricular fibrillation in acute myocardial infarction

To determine the prognosis of late ventricular fibrillation (VF) after acute myocardial infarction (AMI), the length of the monitoring period after AMI was extended. All patients in this series were continuously monitored in a coronary care unit to ensure observation of all VF within 18 days of AMI. From 1977 to 1985, 4,269 patients were admitted with AMI and 413 (9.6%) had in-hospital VF. Of these 281 (6.8%) had early VF (less than 48 hours after AMI) and 132 (3.2%) had late VF (greater than or equal to 48 hours after AMI). In-hospital mortality was 50 and 54% for early and late VF, respectively (p = 0.31). Kaplan-Meier survival analysis showed better survival after discharge for patients with early versus late VF (p = 0.009) but this difference was fully explained by the presence of heart failure. Survival analysis showed the same prognosis after 1, 3 and 5 years for early and late VF, when VF was not associated with heart failure. When VF was associated with heart failure (secondary VF) early VF had a greater mortality than late VF after 2 and 5 years. Logistic regression analysis showed that heart failure (relative risk 1.9 [1.1 to 3.1]) and cardiogenic shock (relative risk 3.9 [1.8 to 8.5]) were significant risk factors for in-hospital death. Late VF compared to early VF had no prognostic implication (relative risk 1.0 [0.6 to 1.6]). For patients discharged from the hospital, risk factors were heart failure (1.8 [1.1 to 2.8]) and previous AMI (1.6 [1.3 to 2.1]).(ABSTRACT TRUNCATED AT 250 WORDS)

[Propofol and 3-in-1 block in ambulatory varix surgery]

A method of anaesthesia for surgical treatment of varicose veins is presented. This consists of a combination of propofol and three-in-one blockade. In a non-blind, non-randomised series, this method was accepted just as well as epidural analgesia or general anaesthesia. The method is recommended for outpatient surgical treatment of varicose veins on account of rapid waking of the patients, reduced need for observation after anaesthesia and reduced pollution with anaesthetic gases in the operation theatre.