Atomic structure and hierarchical assembly of a cross-β amyloid fibril

The cross-β amyloid form of peptides and proteins represents an archetypal and widely accessible structure consisting of ordered arrays of β-sheet filaments. These complex aggregates have remarkable chemical and physical properties, and the conversion of normally soluble functional forms of proteins into amyloid structures is linked to many debilitating human diseases, including several common forms of age-related dementia. Despite their importance, however, cross-β amyloid fibrils have proved to be recalcitrant to detailed structural analysis. By combining structural constraints from a series of experimental techniques spanning five orders of magnitude in length scale—including magic angle spinning nuclear magnetic resonance spectroscopy, X-ray fiber diffraction, cryoelectron microscopy, scanning transmission electron microscopy, and atomic force microscopy—we report the atomic-resolution (0.5 Å) structures of three amyloid polymorphs formed by an 11-residue peptide. These structures reveal the details of the packing interactions by which the constituent β-strands are assembled hierarchically into protofilaments, filaments, and mature fibrils.It is well established that a wide variety of peptides or proteins without any evident sequence similarity can self-assemble into amyloid fibrils (1, 2). These structures have many common characteristics, typically being 100–200 Å in diameter and containing a universal “cross-β” core structure composed of arrays of β-sheets running parallel to the long axis of the fibrils (3). These fibrillar states are highly ordered, with persistence lengths of the order of microns (4) and mechanical properties comparable to those of steel and dragline silk, and much greater than those typical of biological filaments such as actin and microtubules (5). Amyloid fibrils can also possess very high kinetic and thermodynamic stabilities, often exceeding those of the functional folded states of proteins (6), as well as a greater resistance to degradation by chemical or biological means (7). Several functional forms of proteins that exploit these properties have been observed in biological systems (8). More generally, however, the conversion of normally soluble functional proteins into the amyloid state is associated with many debilitating human disorders, ranging from Alzheimer’s disease to type II diabetes (1, 9). Our understanding of the nature of this type of filamentous aggregate has greatly improved in recent years (3, 10–19), particularly through the structural determination of their elementary β-strand building blocks (20) and the characterization of their assembly into cross-β steric zippers (21, 22). However, a thorough understanding of the hierarchical assembly of these individual structural elements into fully-formed fibrils, which display polymorphism but possess a range of generic features (23), has so far been limited by the absence of a complete atomic-resolution cross-β amyloid structures (2).We report here the simultaneous determination of the atomic-resolution structures of a cross-β amyloid fibril and two polymorphic variants, formed by an 11-residue fragment of the protein transthyretin, TTR(105–115) (20). These fibrils have the classic amyloid morphology, being 100–200 Å in diameter and typically 1–3 µm in length (SI Appendix, Fig. S1). We have achieved this objective by bringing together a set of complementary biophysical techniques to provide atomic structures of these complex aggregates. Specifically, we have combined interatomic structural restraints from magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy with high-resolution electron density maps from cryoelectron microscopy (cryo-EM), together with data from X-ray fiber diffraction, scanning transmission electron microscopy (STEM), and atomic force microscopy (AFM) measurements. Our results reveal the molecular basis of the stability and polymorphism of these amyloid fibrils by defining at high resolution the variety of structural elements in their hierarchical self-assembly.     

Quality of care in nursing homes: from the resident's perspective

This paper derives from a study conducted by the Deakin Institute of Nursing Research between 1988 and 1990, whose major objective was to determine the impact of staffing mix on nursing residents' quality of care and life Resident satisfaction with life in the nursing home is a key element in determining the quality of care and quality of life provided Both the literature review and the study objectives supported the view that resident outcome can be collected through assessing the quality of care and the quality of life, through assessment by informed observers using instruments derived from explicitly stated standards, and through eliciting the perceptions of residents themselves A schedule designed to measure satisfaction with care was developed and resident interviews were undertaken using this measure and the Life Satisfaction Index (A) The majority of responses to the resident satisfaction schedule were positive The high percentage of positive responses did not correlate with the observations of the research assistants and there was some concern that while residents were able to assess care they were reluctant to criticize the staff or their behaviour     

The pace of repeated childbearing among young American mothers

Women who first give birth at ages 16 and younger are more likely to bear a second child within the next two years (26 percent) than are women who have their first child at ages 17-18 (20 percent) or at ages 19-22 (22 percent). However, there are important racial and ethnic differences in the likelihood of rapid repeated childbearing: Among whites, age at first birth has little effect on the proportions who have a second birth quickly; but among blacks, it has a significant inverse effect, with younger women more likely than older women to have a second child quickly. At nearly all ages at first birth, Hispanic mothers are more likely than either whites or blacks to have a second birth soon after the first. While the youngest black mothers (those 16 and under) are more likely than the youngest whites to have a rapid second birth, the oldest white mothers (those 19-22) are more likely than the oldest blacks. Socioeconomic background (represented by level of parental education), marital status at first birth and wantedness of the first birth also affect the pace of repeated childbearing. Compared with young mothers whose own mothers are high school graduates, those whose mothers are dropouts are more likely to have a second child within two years. Teenage mothers who are married at their first birth appear somewhat more likely than their unmarried counterparts to bear another child quickly; and mothers who wanted their first child at the time of conception are generally more likely to do so than are mothers whose first births were unwanted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Autologous blood collection in anemic patients using low-dose erythropoietin therapy.

Autologous donation of blood for use during elective surgery is being recommended and used more frequently. Autologous donation and transfusion represent the safest way to handle elective surgical blood requirements because they eliminate the risk of transfusion-transmitted disease and alloimmunization, and significantly reduce the other risks associated with homologous transfusion. Many individuals, particularly women and the elderly, do not have sufficient initial hemoglobin concentration or hemopoietic reserve to effectively use autologous donation. Use of standard-dose recombinant human erythropoietin (rHuEPO) (600 units/kg) to mitigate these limitations is costly. The optimal dose, interval, and route of administration for rHuEPO therapy has yet to be perfected. This article describes a program using low-dose (< 100 units/kg) rHuEPO and also discusses the effectiveness, cost savings, and clinical indications for the use of low-dose rHuEPO.