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Anti-bacterial and anti-viral neuraminidase agents inhibit neuraminidase activity catalyzing the hydrolysis of terminal N -acetylneuraminic acid (Neu5Ac) from glycoconjugates and help to prevent the host pathogenesis that lead to fatal infectious diseases including influenza, bacteremia, sepsis, and cholera. Emerging antibiotic and drug resistances to commonly used anti-neuraminidase agents such as oseltamivir (Tamiflu) and zanamivir (Relenza) have highlighted the need to develop new anti-neuraminidase drugs. We obtained a serendipitous complex crystal of the catalytic domain of Clostridium perfringens neuraminidase ( Cp NanI CD ) with 2-(cyclohexylamino)ethanesulfonic acid (CHES) as a buffer. Here, we report the crystal structure of Cp NanI CD in complex with CHES at 1.24 Å resolution. Amphipathic CHES binds to the catalytic site of Cp NanI CD similar to the substrate (Neu5Ac) binding site. The 2-aminoethanesulfonic acid moiety and cyclohexyl groups of CHES interact with the cluster of three arginine residues and with the hydrophobic pocket of the Cp NanI CD catalytic site. In addition, a structural comparison with other bacterial and human neuraminidases suggests that CHES could serve as a scaffold for the development of new anti-neuraminidase agents targeting Cp NanI. [ABSTRACT FROM AUTHOR]

A hallmark of Alzheimer's disease (AD) is amyloid-β (Aβ) plaque deposition in the brain, causing deficits in cognitive function. Amyloid-beta oligomers (AβOs), the soluble precursor peptides producing Aβ plaques, also produce neurotoxicity and microgliosis together with glycolytic reprogramming. Recently, monocarboxylate transporter 1 (MCT1), a key glycolysis regulator, and its ancillary protein, CD147, are found to play an important role in the secretion of exosomes, 30–200 nm vesicles in size, which are considered as toxic molecule carriers in AD. However, the effect of low-concentration AβOs (1 nM) on microglia MCT1 and CD147 expression as well as 1 nM AβOs-treated microglia-derived exosomes on neuronal toxicity remain largely elusive. In this study, 1 nM AβOs induce significant axonopathy and microgliosis. Furthermore, 1 nM AβOs-treated neurons- or microglia-derived exosomes produce axonopathy through their autologous or heterologous uptake by neurons, supporting the role of exosomes as neurotoxicity mediators in AD. Interestingly, MCT1 and CD147 are enhanced in microglia by treatment with 1 nM AβOs or exosomes from 1 nM AβOs-treated- microglia or neurons, suggesting the implication of AβOs-induced enhanced MCT1 and CD147 in microglia with AD neuropathogenesis, which is consistent with the in-silico analysis of the single cell RNA sequencing data from microglia in mouse models of AD and AD patients. Schematic Diagram. Proposed hypothesis for low level of soluble AβOs (1 nM) directly inducing neuronal damage or indirectly producing damage in neurons by microglia and microglia-derived exosomes. Uptake of AβOs or AβOs-treated neurons-derived exosomes by microglia induce their phenotypic transition into gliosis phenotype together with upregulation of MCT1 and CD147. Importantly, not only autologous uptake of AβOs-treated neurons-derived exosomes by neurons, but also heterologous uptake of AβOs-treated microglia-derived exosomes by neurons produce significant neurotoxicity, supporting the exosome-mediated spreading and amplification of Alzheimer's disease pathogenesis. [Display omitted] • Induction of axonopathy and microgliosis by treatment with AβOs at very low concentration (1 nM). • Production of toxicity in neurons by the uptake of exosomes derived from 1 nM AβOs treated-neurons or microglia. • Enhanced MCT1 and CD147 in microglia by 1 nM AβOs or exosomes from 1 nM AβOs treated-neurons or microglia. • In silico analysis of upregulated MCT1 and CD147 in microglia from mouse models of AD and AD patients. [ABSTRACT FROM AUTHOR]

EF-hand domain-containing protein D2/Swiprosin-1 (EFhd2) is an actin-binding protein mainly expressed in the central nervous and the immune systems of mammals. Intracellular events linked to EFhd2, such as membrane protrusion formation, cell adhesion, and BCR signaling, are triggered by the association of EFhd2 and F-actin. We previously reported that Ca 2+ enhances the F-actin-bundling ability of EFhd2 through maintaining a rigid parallel EFhd2-homodimer structure. It was also reported that the F-actin-bundling ability of EFhd2 is regulated by a phosphorylation-dependent mechanism. EGF-induced phosphorylation at Ser183 of EFhd2 has been shown to inhibit F-actin-bundling, leading to irregular actin dynamics at the leading edges of cells. However, the underlying mechanism of this inhibition has remained elusive. Here, we report the crystal structure of a phospho-mimicking mutant (S183E) of the EFhd2 core domain, where the actin-binding sites are located. Although the overall structure of the phospho-mimicking mutant is similar to the one of the unphosphorylated form, we observed a conformational transition from ordered to disordered structure in the linker region at the C-terminus of the mutant. Based on our structural and biochemical analyses, we suggest that phosphorylation at Ser183 of EFhd2 causes changes in the local conformational dynamics and the surface charge distribution of the actin-binding site, resulting in a re-coordination of the actin-binding sites in the dimer structure and a reduction of F-actin-bundling activity without affecting the F-actin-binding capacity. [ABSTRACT FROM AUTHOR]