The accumulation of metal ions and amyloid-β (Aβ) aggregates found in the brain of patients with Alzheimer's disease (AD) has been suggested to be involved in AD pathogenesis. To investigate metal-Aβ-associated pathways in AD, development of chemical tools to target metal-Aβ species is desired. Only a few efforts, however, have been reported. Here, we report bifunctional small molecules, N-(pyridin-2-ylmethyl)aniline (L2-a) and N 1 ,N 1 -dimethyl-N 4 -(pyridin-2-ylmethyl)benzene-1,4-diamine (L2-b) that can interact with both metal ions and Aβ species, as determined by spectroscopic methods including high-resolution NMR spectroscopy. Using the bifunctional compound L2-b, metal-induced Aβ aggregation and neurotoxicity were modulated in vitro as well as in human neuroblastoma cells. Furthermore, treatment of human AD brain tissue homogenates containing metal ions and Aβ species with L2-b showed disassembly of Aβ aggregates. Therefore, our studies presented herein demonstrate the value of bifunctional compounds as chemical tools for investigating metal-Aβ-associated events and their mechanisms in the development and pathogenesis of AD and as potential therapeutics.amyloid-β peptide | copper | zinc | reactive oxygen species | rational structure-based design M ore than 24 million people worldwide have Alzheimer's disease (AD), a devastating and fatal form of dementia (1-3). The key pathological markers in AD are amyloid-β (Aβ) plaques and neurofibrillary tangles, the accumulation of which is accompanied by oxidative stress, inflammation, and neurodegeneration. The "amyloid hypothesis" in AD states that Aβ, generated via cleavage of the amyloid precursor protein (APP) by β-and γ-secretases, is a proximal causative agent (1-4). It is, however, still unclear which morphological Aβ species, from soluble small oligomers to large fibrils, are central to AD pathogenesis (1-5).In addition to Aβ aggregate deposits, dyshomeostasis and miscompartmentalization of metal ions such as Fe, Cu, and Zn ions clearly occur in AD brains (1-4, 6-10). Some studies suggest that highly concentrated metal ions play an important role in Aβ aggregate deposition and neurotoxicity including the formation of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) (1-4, 6-13). The role of metal ions in AD and molecular mechanisms of metal-Aβ-associated pathological pathways, however, are not fully understood. Using traditional metal chelating agents, potential regulation of metal-induced Aβ aggregation and neurotoxicity has been shown in vitro and in vivo (1-4, 6, 10, 13-17). Some compounds such as clioquinol (CQ) and an 8-hydroxyquinoline derivative (PBT2) have moved into clinical trials and showed improved cognition. Long-term use of CQ is, however, limited by an adverse side effect, subacute myelo-optic neuropathy (18). Although these traditional metal chelators have yet to be available as therapeutic agents, the studies using these compounds show the possible involvement of metal ions in AD pathogenesis.To elucidate the pathological ...

Despite the significance of Alzheimer's disease, the link between metal-associated amyloid-β (metal-Aβ) and disease etiology remains unclear. To elucidate this relationship, chemical tools capable of specifically targeting and modulating metal-Aβ species are necessary, along with a fundamental understanding of their mechanism at the molecular level. Herein, we investigated and compared the interactions and reactivities of the green tea extract, (−)-epigallocatechin-3-gallate [(2R,3R)-5,7-dihydroxy-2-(3,4,5-trihydroxyphenyl)-3,4-dihydro-2H-1-benzopyran-3-yl 3,4,5-trihydroxybenzoate; EGCG], with metal [Cu(II) and Zn(II)]-Aβ and metal-free Aβ species. We found that EGCG interacted with metal-Aβ species and formed small, unstructured Aβ aggregates more noticeably than in metal-free conditions in vitro. In addition, upon incubation with EGCG, the toxicity presented by metalfree Aβ and metal-Aβ was mitigated in living cells. To understand this reactivity at the molecular level, structural insights were obtained by ion mobility-mass spectrometry (IM-MS), 2D NMR spectroscopy, and computational methods. These studies indicated that (i) EGCG was bound to Aβ monomers and dimers, generating more compact peptide conformations than those from EGCGuntreated Aβ species; and (ii) ternary EGCG-metal-Aβ complexes were produced. Thus, we demonstrate the distinct antiamyloidogenic reactivity of EGCG toward metal-Aβ species with a structurebased mechanism.amyloid-β peptide | metal ions | natural products | amyloidogenesis T he brain of individuals with Alzheimer's disease (AD) has protein aggregates composed of misfolded amyloid-β (Aβ) peptides (1-4). The Aβ peptides are produced endogenously through enzymatic cleavage of amyloid precursor protein. Aβ monomers can misfold and oligomerize into various intermediates before the formation and elongation of fibrils that exhibit a characteristic cross-β-sheet structure (1-4). The accumulation of aggregated Aβ species has been a key feature of the amyloid cascade hypothesis, which cites that these aggregates are possible causative agents in AD. In addition, transition metals, such as Cu and Zn, whose misregulation leads to aberrant neuronal function, have a suggested link to AD pathology (1,(3)(4)(5)(6)(7)(8). In vitro and in vivo studies have provided evidence for the direct interactions of metal ions with Aβ and their presence within Aβ plaques, indicating the formation of metal-associated Aβ (metal-Aβ) species. These metal-Aβ species have been implicated in processes that could lead to neurotoxicity (e.g., metal-induced Aβ aggregation and metal-Aβ-mediated reactive oxygen species generation) (1, 3-8). The involvement of metal-Aβ species in AD pathogenesis, however, has not been clearly elucidated. To advance our understanding of the potential neurotoxicity of metal-Aβ species, efforts to develop chemical tools capable of interacting directly with metal-Aβ species and modulating their reactivity in vitro and in biological systems are under way (1,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)...

We analyzed 6,749 lines tagged by the gene trap vector pGA2707. This resulted in the isolation of 3,793 genomic sequences flanking the T-DNA. Among the insertions, 1,846 T-DNAs were integrated into genic regions, and 1,864 were located in intergenic regions. Frequencies were also higher at the beginning and end of the coding regions and upstream near the ATG start codon. The overall GC content at the insertion sites was close to that measured from the entire rice (Oryza sativa) genome. Functional classification of these 1,846 tagged genes showed a distribution similar to that observed for all the genes in the rice chromosomes. This indicates that T-DNA insertion is not biased toward a particular class of genes. There were 764, 327, and 346 T-DNA insertions in chromosomes 1, 4 and 10, respectively. Insertions were not evenly distributed; frequencies were higher at the ends of the chromosomes and lower near the centromere. At certain sites, the frequency was higher than in the surrounding regions. This sequence database will be valuable in identifying knockout mutants for elucidating gene function in rice. This resource is available to the scientific community at http://www.postech.ac.kr/life/pfg/risd.Insertional mutagenesis is one of the most useful methods for analyzing gene function. When foreign DNA is inserted into a gene, it not only creates a mutation but also tags the affected gene, facilitating its isolation and characterization (Azpiroz-Leehan and Feldmann, 1997). Transposons and T-DNA have been used most widely as an insertional mutagen (Mathur et al., 1998;Wisman et al., 1998; Krysan et al., 1999;Parinov et al., 1999;Speulman et al., 1999;Tissier et al., 1999). It is believed that T-DNA insertion is a random event and that the inserted sequences are stable through multiple generations (Azpiroz- Leehan and Feldmann, 1997;Parinov and Sundaresan, 2000). Insertional mutant pools have been constructed in Arabidopsis and used for functional analysis of a number of genes (Feldmann, 1991; Koncz et al., 1992; Azpiroz-Leehan and Feldmann, 1997; Bechtold and Pelletier, 1998; Krysan et al., 1999; Galbiati et al., 2000;Parinov and Sundaresan, 2000; Bouché and Bouchez, 2001;Sessions et al., 2002;Szabados et al., 2002). The procedure for T-DNA insertional mutagenesis has also been applied to rice (Oryza sativa) using the Agrobacterium tumefaciensmediated transformation method (Hiei et al., 1994). Jeon et al. (2000) have reported the construction of over 20,000 T-DNA-tagged rice lines. A T-DNA insertional mutagen can be modified to trap a gene by inserting a reporter gene, such as gus (␤-glucuronidase), next to the T-DNA border (Sundaresan et al., 1995; Jeon et al., 2000;Springer, 2000). Approximately 5% to 10% of the mutagenized lines are GUS positive, demonstrating the efficiency of this gene-trapping system (Chin et al., 1999; Jeon et al., 2000).Completion of the genome sequencing for both Arabidopsis and rice has provided new reverse genetic means for assigning biological functions to sequenced genes (Kumar...

Amyloid-β (Aβ) peptides and their metal-associated aggregated states have been implicated in the pathogenesis of Alzheimer’s disease (AD). Although the etiology of AD remains uncertain, understanding the role of metal-Aβ species could provide insights into the onset and development of the disease. To unravel this, bifunctional small molecules that can specifically target and modulate metal-Aβ species have been developed, which could serve as suitable chemical tools for investigating metal-Aβ-associated events in AD. Through a rational structure-based design principle involving the incorporation of a metal binding site into the structures of Aβ interacting molecules, we devised stilbene derivatives (L1-a and L1-b) and demonstrated their reactivity toward metal-Aβ species. In particular, the dual functions of compounds with different structural features (e.g., with or without a dimethylamino group) were explored by UV-vis, X-ray crystallography, high-resolution 2D NMR, and docking studies. Enhanced bifunctionality of compounds provided greater effects on metal-induced Aβ aggregation and neurotoxicity in vitro and in living cells. Mechanistic investigations of the reaction of L1-a and L1-b with Zn2+-Aβ species by UV-vis and 2D NMR suggest that metal chelation with ligand and/or metal-ligand interaction with the Aβ peptide may be driving factors for the observed modulation of metal-Aβ aggregation pathways. Overall, the studies presented herein demonstrate the importance of a structure-interaction-reactivity relationship for designing small molecules to target metal-Aβ species allowing for the modulation of metal-induced Aβ reactivity and neurotoxicity.

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Translesion DNA synthesis (TLS) by specialized DNA polymerases (Pols) is a conserved mechanism for tolerating replication blocking DNA lesions. The actions of TLS Pols are managed in part by ring-shaped sliding clamp proteins. In addition to catalyzing TLS, altered expression of TLS Pols impedes cellular growth. The goal of this study was to define the relationship between the physiological function of Escherichia coli Pol IV in TLS and its ability to impede growth when overproduced. To this end, 13 novel Pol IV mutants were identified that failed to impede growth. Subsequent analysis of these mutants suggest that overproduced levels of Pol IV inhibit E. coli growth by gaining inappropriate access to the replication fork via a Pol III-Pol IV switch that is mechanistically similar to that used under physiological conditions to coordinate Pol IV-catalyzed TLS with Pol III-catalyzed replication. Detailed analysis of one mutant, Pol IV-T120P, and two previously described Pol IV mutants impaired for interaction with either the rim (Pol IVR) or the cleft (Pol IVC) of the β sliding clamp revealed novel insights into the mechanism of the Pol III-Pol IV switch. Specifically, Pol IV-T120P retained complete catalytic activity in vitro but, like Pol IVR and Pol IVC, failed to support Pol IV TLS function in vivo. Notably, the T120P mutation abrogated a biochemical interaction of Pol IV with Pol III that was required for Pol III-Pol IV switching. Taken together, these results support a model in which Pol III-Pol IV switching involves interaction of Pol IV with Pol III, as well as the β clamp rim and cleft. Moreover, they provide strong support for the view that Pol III-Pol IV switching represents a vitally important mechanism for regulating TLS in vivo by managing access of Pol IV to the DNA.

This study aimed to confirm the mediating effect of job involvement in the relationship between grit and turnover intention among nurses working at university hospitals. Methods: Participants included 437 nurses from university hospitals located in C city, Gyeongnam. Data were collected from January 8 to 19, 2018, using self-report questionnaires. Data were analyzed using the t-test, analysis of variance, Scheffe's test, Pearson's correlation coefficient, and multiple regression, with the SPSS/22.0 program. A mediation analysis was performed according to the Baron and Kenny, and bootstrapping methods. Results: There were significant relationships between grit and job involvement (r=.40, p<.001), grit and turnover intention (r=-.29, p<.001), and turnover intention and job involvement (r=-.52, p<.001). Job involvement showed partial mediating effects in the relationship between grit and turnover intention. Conclusion: Grit increased job involvement and lowered turnover intention. Therefore, to reduce nurses' turnover intention, it is necessary to develop a program and strategies to increase their grit.

Fundamental study of enzymatic nucleoside transport suffers for lack of optical probes that can be tracked noninvasively. Nucleoside transporters are integral membrane glycoproteins that mediate the salvage of nucleosides and their passage across cell membranes. The substrate recognition site is the deoxyribose sugar, often with little distinction among nucleobases. Reported here are nucleoside analogues in which emissive, cyclometalated iridium(III) complexes are "clicked" to C-1 of deoxyribose in place of canonical nucleobases. The resulting complexes show visible luminescence at room temperature and 77 K with microsecond-length triplet lifetimes. A representative complex is crystallographically characterized. Transport and luminescence are demonstrated in cultured human carcinoma (KB3-1) cells.