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Acta Cryst. (2014). A70, C698
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Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in humans with age being the biggest risk factor. The mechanisms by which the disease progresses to cognitive decline in the sufferer are complex and not fully elucidated. A defining pathological feature is the deposition of extracellular plaques composed primarily of misfolded amyloid beta (Aβ) peptide: a proteolytic breakdown product of the much larger Amyloid Precursor Protein. While Aβ peptides are the main constituents of amyloid plaques that burden the diseased brain, plaque burden correlates poorly with the severity of the disease. There is accumulating evidence that a prefibrillar or protofibrillar soluble form of Aβ can compromise neuronal functions and trigger cell death. Immunotherapy targeting Abeta is a promising direction in AD research with active and passive immunotherapies shown to lower cerebral Aβ levels and rescue cognitive function in animal models. Anti-Aβ immunotherapies are a significant class of AD therapeutics currently in human clinical trials. We have been examining the molecular basis of antibody engagement of Aβ epitopes to inform the analysis of clinical trial data and to guide the engineering of anti-Aβ antibodies with optimised specificity and affinity. We have determined the structures of three different AD antibodies in complex with Ab peptides: (1) WO2, which recognises the N-terminus of Aβ, (2) Mab 2286, which like the AD immunotherapeutic Ponezumab (Pfizer), shows specificity for the C-terminus of Aβ40 but has no significant cross-reactivity with Aβ42/43, and (3) Bapineuzumab, a humanized antibody developed by Pfizer and Johnson & Johnson which recognises the N-terminus of Aβ but cannot recognize N-terminally modified or truncated Aβ peptides (1). All these studies reveal surprising aspects of Aβ peptide recognition by the antibodies and suggest new avenues for AD antibody development.

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Acta Cryst. (2014). A70, C808
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14-3-3 proteins are a highly conserved family of dimeric phospho-serine binding proteins that modulate the functions of key cellular proteins involved in signaling. 14-3-3ζ plays a prominent role in signaling pathways leading to inhibition of apoptosis, sequestration of tumor suppressor proteins and activation of signalling pathways that promote growth. 14-3-3ζ expression is up-regulated in many human cancers and associated with enhanced survival of cancer cells. The significant association of 14-3-3ζ over expression with disease recurrence and chemo-resistance makes this protein an attractive candidate for anti-cancer therapy. The anti-apoptotic activity of 14-3-3ζ is entirely dependent on the dimeric state of the protein. Our studies have shown that 14-3-3ζ activity is regulated by sphingosine and other lipid analogs that render 14-3-3 phosphorylatable, disrupting its dimeric state thereby leading to apoptosis [1]. Structural studies and mutagenesis on 14-3-3ζ confirm that the dimeric state of 14-3-3ζ is stabilized by salt bridges that form across the dimer interface. Based on this we have carried out an in silico screen of a virtual library of drug-like small molecules to identify compounds that bind to the dimer interface of 14-3-3ζ. Candidate small molecules have been assessed for their ability to render 14-3-3ζ phosphorylatable in vitro and consequently we have identified a family of small molecules with 14-3-3ζ dimer-destabilizing properties. These small molecules induce apoptosis in leukemic cells by activating apoptotic mediators known to be regulated by dimeric 14-3-3. We have recently solved the crystal structure of 14-3-3ζ with one of our hit compounds bound at the dimer interface. Our results suggest that relatively small perturbations at the dimer interface, can destabilize the salt bridges that hold 14-3-3 dimers together, thus providing a novel approach to targeting 14-3-3 proteins for therapeutic benefit.
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