Oxidative stress induced by reactive oxygen species (ROS) is one of the major toxicity mechanisms of engineered nanoparticles (NPs). To advance our knowledge of the photogeneration of ROS on NPs, this Letter reports the ROS generation kinetics of uncoated silver (AgNPs), gold (AuNPs), nickel (NiNPs), and silicon (SiNPs) NPs in aqueous suspension under UV irradiation (365 nm) and analyzes the potential ROS photogeneration mechanisms as well as the associated antibacterial effects. The results showed that AgNPs generated superoxide and hydroxyl radicals, whereas AuNPs, NiNPs, and SiNPs generated only singlet oxygen. The electronic structure and redox potentials of SiNPs were shown to mediate ROS generation. By contrast, ROS generation on AuNPs, AgNPs, and NiNPs was primarily due to surface plasmon resonance. The antibacterial activities of these NPs toward E. coli cells under UV irradiation were AgNPs (strongest) > SiNPs > NiNPs > AuNPs. ROS generation and metal ion release significantly enhanced the NPs' antibacterial activity.
Summary Mitochondria need to be juxtaposted to phagosomes to synergistically produce ample reactive oxygen species (ROS) in phagocytes for pathogens killing. However, how phagosomes transmit signal to recruit mitochondria remains unclear. Here, we report that the kinases Mst1 and Mst2 function to control ROS production by regulating mitochondrial trafficking and mitochondrion-phagosome juxtaposition. Mst1 and Mst2 activate Rac GTPase to promote Toll-like receptor (TLR)-triggered assembly of the TRAF6-ECSIT complex that is required for mitochondrial recruitment to phagosomes. Inactive forms of Rac, including the human Rac2D57N mutant, disrupt the TRAF6-ECSIT complex by sequestering TRAF6, and severely dampen ROS production and greatly increase susceptibility to bacterial infection. These findings demonstrate the TLR-Mst1-Mst2-Rac signalling axis to be critical for effective phagosome-mitochondrion function and bactericidal activity.
Telomerase extends chromosome ends by copying a short template sequence within its intrinsic RNA component. Telomerase RNA (TR) from different groups of species varies dramatically in sequence and size. We report here the bioinformatic identification, secondary structure comparison, and functional analysis of the smallest known vertebrate TRs from five teleost fishes. The teleost TRs (312-348 nucleotides) are significantly smaller than the cartilaginous fish TRs (478 -559 nucleotides) and tetrapod TRs. This remarkable length reduction of teleost fish TRs correlates positively with the genome size, reflecting an unusual structural plasticity of TR during evolution. The teleost TR consists of a compact three-domain structure, lacking most of the sequences in regions that are variable in other vertebrate TR structures. The medaka and fugu TRs, when assembled with their telomerase reverse transcriptase (TERT) protein counterparts, reconstituted active and processive telomerase enzymes. Titration analysis of individual RNA domains suggests that the efficient assembly of the telomerase complex is influenced more by the telomerase reverse transcriptase (TERT) binding of the CR4 -CR5 domain than the pseudoknot domain of TR. The remarkably small teleost fish TR further expands our understanding about the evolutionary divergence of vertebrate TR.Telomeres are specialized DNA-protein complexes that cap chromosome ends and are important for genome stability and cellular proliferation (1). Telomeres consist of repetitive DNA sequences and a variety of telomere-associated proteins. The length of telomeric DNA in most eukaryotes is maintained by telomerase, a specialized reverse transcriptase that synthesizes telomeric DNA repeats at chromosome ends to counterbalance the natural shortening that occurs during DNA replication. Telomerase, a ribonucleoprotein (RNP) 2 enzyme, consists of at least two essential core components, the catalytic protein component telomerase reverse transcriptase (TERT), and the telomerase RNA (TR) that provides a template for telomeric DNA synthesis. TR is remarkably variable in size, sequence, and even secondary structure between different groups of eukaryotes. To date, TR sequences have been identified in 28 ciliates, 14 yeasts, and 38 vertebrates. Due to the lack of sequence similarity between groups of species, the TR secondary structures were determined independently for each of these three groups (2). The vertebrate TR secondary structure is composed of three highly conserved structural domains: the pseudoknot/template domain, the CR4 -CR5 domain, and the scaRNA domain (3-5). The pseudoknot/template domain contains a template region for telomeric DNA synthesis, and a conserved pseudoknot structure essential for telomerase activity. The CR4 -CR5 domain together with the pseudoknot/template domain are both required for reconstituting active telomerase in vitro (6). However, their mechanistic roles are unclear. The scaRNA domain is crucial for the 3Ј-end processing of TR and telomerase RNP biogenesi...
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