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      Structure of Crenezumab Complex with Aβ Shows Loss of β-Hairpin

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          Abstract

          Accumulation of amyloid-β (Aβ) peptides and amyloid plaque deposition in brain is postulated as a cause of Alzheimer’s disease (AD). The precise pathological species of Aβ remains elusive although evidence suggests soluble oligomers may be primarily responsible for neurotoxicity. Crenezumab is a humanized anti-Aβ monoclonal IgG4 that binds multiple forms of Aβ, with higher affinity for aggregated forms, and that blocks Aβ aggregation, and promotes disaggregation. To understand the structural basis for this binding profile and activity, we determined the crystal structure of crenezumab in complex with Aβ. The structure reveals a sequential epitope and conformational requirements for epitope recognition, which include a subtle but critical element that is likely the basis for crenezumab’s versatile binding profile. We find interactions consistent with high affinity for multiple forms of Aβ, particularly oligomers. Of note, crenezumab also sequesters the hydrophobic core of Aβ and breaks an essential salt-bridge characteristic of the β-hairpin conformation, eliminating features characteristic of the basic organization in Aβ oligomers and fibrils, and explains crenezumab’s inhibition of aggregation and promotion of disaggregation. These insights highlight crenezumab’s unique mechanism of action, particularly regarding Aβ oligomers, and provide a strong rationale for the evaluation of crenezumab as a potential AD therapy.

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          Shape complementarity at protein/protein interfaces.

          A new statistic Sc, which has a number of advantages over other measures of packing, is used to examine the shape complementarity of protein/protein interfaces selected from the Brookhaven Protein Data Bank. It is shown using Sc that antibody/antigen interfaces as a whole exhibit poorer shape complementarity than is observed in other systems involving protein/protein interactions. This result can be understood in terms of the fundamentally different evolutionary history of particular antibody/antigen associations compared to other systems considered, and in terms of the differing chemical natures of the interfaces.
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            A structural model for Alzheimer's beta -amyloid fibrils based on experimental constraints from solid state NMR.

            We present a structural model for amyloid fibrils formed by the 40-residue beta-amyloid peptide associated with Alzheimer's disease (Abeta(1-40)), based on a set of experimental constraints from solid state NMR spectroscopy. The model additionally incorporates the cross-beta structural motif established by x-ray fiber diffraction and satisfies constraints on Abeta(1-40) fibril dimensions and mass-per-length determined from electron microscopy. Approximately the first 10 residues of Abeta(1-40) are structurally disordered in the fibrils. Residues 12-24 and 30-40 adopt beta-strand conformations and form parallel beta-sheets through intermolecular hydrogen bonding. Residues 25-29 contain a bend of the peptide backbone that brings the two beta-sheets in contact through sidechain-sidechain interactions. A single cross-beta unit is then a double-layered beta-sheet structure with a hydrophobic core and one hydrophobic face. The only charged sidechains in the core are those of D23 and K28, which form salt bridges. Fibrils with minimum mass-per-length and diameter consist of two cross-beta units with their hydrophobic faces juxtaposed.
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              2015 Alzheimer's disease facts and figures.

              (2015)
              This report discusses the public health impact of Alzheimer’s disease (AD), including incidence and prevalence, mortality rates, costs of care and the overall effect on caregivers and society. It also examines the challenges encountered by health care providers when disclosing an AD diagnosis to patients and caregivers. An estimated 5.3 million Americans have AD; 5.1 million are age 65 years, and approximately 200,000 are age <65 years and have younger onset AD. By mid-century, the number of people living with AD in the United States is projected to grow by nearly 10 million, fueled in large part by the aging baby boom generation. Today, someone in the country develops AD every 67 seconds. By 2050, one new case of AD is expected to develop every 33 seconds, resulting in nearly 1 million new cases per year, and the estimated prevalence is expected to range from 11 million to 16 million. In 2013, official death certificates recorded 84,767 deaths from AD, making AD the sixth leading cause of death in the United States and the fifth leading cause of death in Americans age 65 years. Between 2000 and 2013, deaths resulting from heart disease, stroke and prostate cancer decreased 14%, 23% and 11%, respectively, whereas deaths from AD increased 71%. The actual number of deaths to which AD contributes (or deaths with AD) is likely much larger than the number of deaths from AD recorded on death certificates. In 2015, an estimated 700,000 Americans age 65 years will die with AD, and many of them will die from complications caused by AD. In 2014, more than 15 million family members and other unpaid caregivers provided an estimated 17.9 billion hours of care to people with AD and other dementias, a contribution valued at more than $217 billion. Average per-person Medicare payments for services to beneficiaries age 65 years with AD and other dementias are more than two and a half times as great as payments for all beneficiaries without these conditions, and Medicaid payments are 19 times as great. Total payments in 2015 for health care, long-term care and hospice services for people age 65 years with dementia are expected to be $226 billion. Among people with a diagnosis of AD or another dementia, fewer than half report having been told of the diagnosis by their health care provider. Though the benefits of a prompt, clear and accurate disclosure of an AD diagnosis are recognized by the medical profession, improvements to the disclosure process are needed. These improvements may require stronger support systems for health care providers and their patients.
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                20 December 2016
                2016
                : 6
                : 39374
                Affiliations
                [1 ]Genentech, Inc., 1 DNA Way , South San Francisco, California 94080, USA
                [2 ]AC Immune SA, EPFL Innovation Park, Building B , 1015 Lausanne, Switzerland
                Author notes
                Article
                srep39374
                10.1038/srep39374
                5171940
                27996029
                3789f8e0-73d6-493d-b61d-3feaf2ee7224
                Copyright © 2016, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 20 May 2016
                : 21 November 2016
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