The aggregation-enhancing huntingtin N-terminus is helical in amyloid fibrils

The 17-residue N-terminus (httNT) directly flanking the polyQ sequence in huntingtin (htt) N-terminal fragments plays a crucial role in initiating and accelerating the aggregation process that is associated with Huntington's disease pathogenesis. Here we report on magic-angle-spinning solid-state NMR studies of the amyloid-like aggregates of an htt N-terminal fragment. We find that the polyQ portion of this peptide exists in a rigid, dehydrated amyloid core that is structurally similar to simpler polyQ fibrils and may contain antiparallel β-sheets. In contrast, the httNT sequence in the aggregates is composed in part of a well-defined helix, which likely also exists in early oligomeric aggregates. Further NMR experiments demonstrate that the N-terminal helical segment displays increased dynamics and water exposure. Given its specific contribution to the initiation, rate, and mechanism of fibril formation, the helical nature of httNT and its apparent lack of effect on the polyQ fibril core structure seem surprising. The results provide new details about these disease-associated aggregates and also provide a clear example of an amino acid sequence that greatly enhances the rate of amyloid formation while itself not taking part in the amyloid structure. There is an interesting mechanistic analogy to recent reports pointing out the early-stage contributions of transient intermolecular helix-helix interactions in the aggregation behavior of various other amyloid fibrils. © 2011 American Chemical Society

Amyloid-like fibrils from a domain-swapping protein feature a parallel, in-register conformation without native-like interactions

The formation of amyloid-like fibrils is characteristic of various diseases, but the underlying mechanism and the factors that determine whether, when, and how proteins form amyloid, remain uncertain. Certain mechanisms have been proposed based on the three-dimensional or runaway domain swapping, inspired by the fact that some proteins show an apparent correlation between the ability to form domain-swapped dimers and a tendency to form fibrillar aggregates. Intramolecular β-sheet contacts present in the monomeric state could constitute intermolecular β-sheets in the dimeric and fibrillar states. One example is an amyloid-forming mutant of the immunoglobulin binding domain B1 of streptococcal protein G, which in its native conformation consists of a four-stranded β-sheet and one α-helix. Under native conditions this mutant adopts a domainswapped dimer, and it also forms amyloid-like fibrils, seemingly in correlation to its domain-swapping ability. We employ magic angle spinning solid-state NMR and other methods to examine key structural features of these fibrils. Our results reveal a highly rigid fibril structure that lacks mobile domains and indicate a parallel in-register β-sheet structure and a general loss of native conformation within the mature fibrils. This observation contrasts with predictions that native structure, and in particular intermolecular β-strand interactions seen in the dimeric state, may be preserved in "domain-swapping" fibrils. We discuss these observations in light of recent work on related amyloidforming proteins that have been argued to follow similar mechanisms and how this may have implications for the role of domain-swapping propensities for amyloid formation. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc

Pre-Interventional Cardiac and ECG Changes in Acute Organophosphate Poisoning Cases Admitted to a Tertiary Hospital in India

Background: Cardiac complications are the less common fatal effect of acute organophosphate poisoning. This study was undertaken to analyze the pre-interventional cardiac and Electrocardiographic (ECG) changes in acute organophosphate poisoning cases.Materials and Methods: Clinical records of acute organophosphate poisoning patients of age less than 50 years admitted to KLE’s Dr. Prabhakar Kore Hospital, Belgaum, Karnataka, from 01-01-2010 to 31-12-2010 were analyzed. Cases of organophosphate poisonings referred from other hospitals, poisoning with multiple agents, patients with history of previous cardiac diseases and coexisting medical conditions were excluded from the study. Poisoning Severity Score was calculated as per International Programme on Chemical Safety and patients were grouped into 3 grades.Results: In this study, 50 cases of acute organophosphate poisoning (male - 32; female - 18) were analyzed. Sinus tachycardia was present in 45 patients (90%), hypertension in 13 (26%) and hypotension in 12 (24%). Prolonged corrected QT interval was observed in 14 patients (28%), elevated ST segment in 2 (4%), inverted T wave in 13 (26%) and conduction defects in 1 (2%). Among 14 patients with prolonged corrected QT interval, 12 were in grade III and 2 in grade II severity; and, among 13 patients who had inverted T wave, 2 were in grade I, 4 in grade II and 7 in grade III severity. Acidosis, as assessed by blood pH and HCO3, was observed in 22 patients (44%).Conclusion: Fatal cardiac complications do occur in acute organophosphate poisoning, which are overlooked at times as the most common complications expected are respiratory complications. Higher incidence of ECG changes in Grade III cases suggests that if the cardiac complications develop, the patient should be immediately transferred to an intensive cardiac care unit

Fibril polymorphism affects immobilized non-amyloid flanking domains of huntingtin exon1 rather than its polyglutamine core

Polyglutamine expansion in the huntingtin protein is the primary genetic cause of Huntington's disease (HD). Fragments coinciding with mutant huntingtin exon1 aggregate in vivo and induce HD-like pathology in mouse models. The resulting aggregates can have different structures that affect their biochemical behaviour and cytotoxic activity. Here we report our studies of the structure and functional characteristics of multiple mutant htt exon1 fibrils by complementary techniques, including infrared and solid-state NMR spectroscopies. Magic-angle-spinning NMR reveals that fibrillar exon1 has a partly mobile α-helix in its aggregation-accelerating N terminus, and semi-rigid polyproline II helices in the proline-rich flanking domain (PRD). The polyglutamine-proximal portions of these domains are immobilized and clustered, limiting access to aggregation-modulating antibodies. The polymorphic fibrils differ in their flanking domains rather than the polyglutamine amyloid structure. They are effective at seeding polyglutamine aggregation and exhibit cytotoxic effects when applied to neuronal cells

Molecular basis for passive immunotherapy of Alzheimer's disease

Amyloid aggregates of the amyloid-{beta} (A{beta}) peptide are implicated in the pathology of Alzheimer's disease. Anti-A{beta} monoclonal antibodies (mAbs) have been shown to reduce amyloid plaques in vitro and in animal studies. Consequently, passive immunization is being considered for treating Alzheimer's, and anti-A{beta} mAbs are now in phase II trials. We report the isolation of two mAbs (PFA1 and PFA2) that recognize A{beta} monomers, protofibrils, and fibrils and the structures of their antigen binding fragments (Fabs) in complex with the A{beta}(1–8) peptide DAEFRHDS. The immunodominant EFRHD sequence forms salt bridges, hydrogen bonds, and hydrophobic contacts, including interactions with a striking WWDDD motif of the antigen binding fragments. We also show that a similar sequence (AKFRHD) derived from the human protein GRIP1 is able to cross-react with both PFA1 and PFA2 and, when cocrystallized with PFA1, binds in an identical conformation to A{beta}(1–8). Because such cross-reactivity has implications for potential side effects of immunotherapy, our structures provide a template for designing derivative mAbs that target A{beta} with improved specificity and higher affinity

Impact of the COVID-19 pandemic on interventional cardiology fellowship training in the New York metropolitan area: A perspective from the United States epicenter

© 2020 Wiley Periodicals, Inc. Background: The healthcare burden posed by the coronavirus disease 2019 (COVID-19) pandemic in the New York Metropolitan area has necessitated the postponement of elective procedures resulting in a marked reduction in cardiac catheterization laboratory (CCL) volumes with a potential to impact interventional cardiology (IC) fellowship training. Methods: We conducted a web-based survey sent electronically to 21 Accreditation Council for Graduate Medical Education accredited IC fellowship program directors (PDs) and their respective fellows. Results: Fourteen programs (67%) responded to the survey and all acknowledged a significant decrease in CCL procedural volumes. More than half of the PDs reported part of their CCL being converted to inpatient units and IC fellows being redeployed to COVID-19 related duties. More than two-thirds of PDs believed that the COVID-19 pandemic would have a moderate (57%) or severe (14%) adverse impact on IC fellowship training, and 21% of the PDs expected their current fellows\u27 average percutaneous coronary intervention (PCI) volume to be below 250. Of 25 IC fellow respondents, 95% expressed concern that the pandemic would have a moderate (72%) or severe (24%) adverse impact on their fellowship training, and nearly one-fourth of fellows reported performing fewer than 250 PCIs as of March 1st. Finally, roughly one-third of PDs and IC fellows felt that there should be consideration of an extension of fellowship training or a period of early career mentorship after fellowship. Conclusions: The COVID-19 pandemic has caused a significant reduction in CCL procedural volumes that is impacting IC fellowship training in the NY metropolitan area. These results should inform professional societies and accreditation bodies to offer tailored opportunities for remediation of affected trainees

Folding landscape of mutant huntingtin Exon1: Diffusible multimers, oligomers and fibrils, and no detectable monomer

Expansion of the polyglutamine (polyQ) track of the Huntingtin (HTT) protein above 36 is associated with a sharply enhanced risk of Huntington's disease (HD). Although there is general agreement that HTT toxicity resides primarily in N-terminal fragments such as the HTT exon1 protein, there is no consensus on the nature of the physical states of HTT exon1 that are induced by polyQ expansion, nor on which of these states might be responsible for toxicity. One hypothesis is that polyQ expansion induces an alternative, toxic conformation in the HTT exon1 monomer. Alternative hypotheses posit that the toxic species is one of several possible aggregated states. Defining the nature of the toxic species is particularly challenging because of facile interconversion between physical states as well as challenges to identifying these states, especially in vivo. Here we describe the use of fluorescence correlation spectroscopy (FCS) to characterize the detailed time and repeat length dependent self-association of HTT exon1-like fragments both with chemically synthesized peptides in vitro and with cell-produced proteins in extracts and in living cells. We find that, in vitro, mutant HTT exon1 peptides engage in polyQ repeat length dependent dimer and tetramer formation, followed by time dependent formation of diffusible spherical and fibrillar oligomers and finally by larger, sedimentable amyloid fibrils. For expanded polyQ HTT exon1 expressed in PC12 cells, monomers are absent, with tetramers being the smallest molecular form detected, followed in the incubation time course by small, diffusible aggregates at 6-9 hours and larger, sedimentable aggregates that begin to build up at 12 hrs. In these cell cultures, significant nuclear DNA damage appears by 6 hours, followed at later times by caspase 3 induction, mitochondrial dysfunction, and cell death. Our data thus defines limits on the sizes and concentrations of different physical states of HTT exon1 along the reaction profile in the context of emerging cellular distress. The data provide some new candidates for the toxic species and some new reservations about more well-established candidates. Compared to other known markers of HTT toxicity, nuclear DNA damage appears to be a relatively early pathological event