No abstract

Type I interferon (IFN-I) plays a critical role in the homeostasis of hematopoietic stem cells and influences neutrophil influx to the site of inflammation. IFN-I receptor knockout (Ifnar1 −/−) mice develop significant defects in the infiltration of Ly6Chi monocytes in the lung after influenza infection (A/PR/8/34, H1N1). Ly6Chi monocytes of wild-type (WT) mice are the main producers of MCP-1 while the alternatively generated Ly6Cint monocytes of Ifnar1 −/− mice mainly produce KC for neutrophil influx. As a consequence, Ifnar1 −/− mice recruit more neutrophils after influenza infection than do WT mice. Treatment of IFNAR1 blocking antibody on the WT bone marrow (BM) cells in vitro failed to differentiate into Ly6Chi monocytes. By using BM chimeric mice (WT BM into Ifnar1 −/− and vice versa), we confirmed that IFN-I signaling in hematopoietic cells is required for the generation of Ly6Chi monocytes. Of note, WT BM reconstituted Ifnar1 −/− chimeric mice with increased numbers of Ly6Chi monocytes survived longer than influenza-infected Ifnar1 −/− mice. In contrast, WT mice that received Ifnar1 −/− BM cells with alternative Ly6Cint monocytes and increased numbers of neutrophils exhibited higher mortality rates than WT mice given WT BM cells. Collectively, these data suggest that IFN-I contributes to resistance of influenza infection by control of monocytes and neutrophils in the lung.

Here, we report for the first time cell-permeable and biocompatible polymeric nanoparticles consisting of a polymer conjugated to a near-infrared (NIR) fluorescence (Cy5.5)-linked effector caspase-specific peptide. The close spatial proximity of the NIR fluorochromes in polymeric nanoparticles results in an autoquenched state, but polymer nanoparticles give rise to strong NIR fluorescence signal under apoptotic cells. Thus, the smart polymeric nanoparticle developed here is an attractive probe for real-time imaging of apoptosis in single cells.

While basic mechanisms of several major molecular chaperones are well understood, this machinery has been known to be involved in folding of only limited number of proteins inside the cells. Here, we report a chaperone type of protein folding facilitated by interaction with RNA. When an RNA-binding module is placed at the N-terminus of aggregation-prone target proteins, this module, upon binding with RNA, further promotes the solubility of passenger proteins, potentially leading to enhancement of proper protein folding. Studies on in vitro refolding in the presence of RNA, coexpression of RNA molecules in vivo and the mutants with impaired RNA binding ability suggests that RNA can exert chaperoning effect on their bound proteins. The results suggest that RNA binding could affect the overall kinetic network of protein folding pathway in favor of productive folding over off-pathway aggregation. In addition, the RNA binding-mediated solubility enhancement is extremely robust for increasing soluble yield of passenger proteins and could be usefully implemented for high-throughput protein expression for functional and structural genomic research initiatives. The RNA-mediated chaperone type presented here would give new insights into de novo folding in vivo.

The folding of monomeric antigens and their subsequent assembly into higher ordered structures are crucial for robust and effective production of nanoparticle (NP) vaccines in a timely and reproducible manner. Despite significant advances in in silico design and structure-based assembly, most engineered NPs are refractory to soluble expression and fail to assemble as designed, presenting major challenges in the manufacturing process. The failure is due to a lack of understanding of the kinetic pathways and enabling technical platforms to ensure successful folding of the monomer antigens into regular assemblages. Capitalizing on a novel function of RNA as a molecular chaperone (chaperna: chaperone + RNA), we provide a robust protein-folding vehicle that may be implemented to NP assembly in bacterial hosts. The receptor-binding domain (RBD) of Middle East respiratory syndrome-coronavirus (MERS-CoV) was fused with the RNA-interaction domain (RID) and bacterioferritin, and expressed in Escherichia coli in a soluble form. Site-specific proteolytic removal of the RID prompted the assemblage of monomers into NPs, which was confirmed by electron microscopy and dynamic light scattering. The mutations that affected the RNA binding to RBD significantly increased the soluble aggregation into amorphous structures, reducing the overall yield of NPs of a defined size. This underscored the RNA-antigen interactions during NP assembly. The sera after mouse immunization effectively interfered with the binding of MERS-CoV RBD to the cellular receptor hDPP4. The results suggest that RNA-binding controls the overall kinetic network of the antigen folding pathway in favor of enhanced assemblage of NPs into highly regular and immunologically relevant conformations. The concentration of the ion Fe2+, salt, and fusion linker also contributed to the assembly in vitro, and the stability of the NPs. The kinetic “pace-keeping” role of chaperna in the super molecular assembly of antigen monomers holds promise for the development and delivery of NPs and virus-like particles as recombinant vaccines and for serological detection of viral infections.

Recent studies have revealed that innate immunity is involved in the development of adaptive immune responses; however, its role in protection is not clear. In order to elucidate the exact role of Toll-like receptor (TLR) or RIG-I-like receptor (RLR) signaling on immunogenicity and protective efficacy against influenza A virus infection (A/PR/8/34 [PR8]; H1N1), we adapted several innate signal-deficient mice (e.g., TRIF and IPS-1 ؊/؊ ). In this study, we found that MyD88 signaling was required for recruitment of CD11b؉ granulocytes, production of early inflammatory cytokines, optimal proliferation of CD4 T cells, and production of Th1 cytokines by T cells. However, PR8 virus-specific IgG and IgA antibody levels in both systemic and mucosal compartments were normal in TLR-and RLRdeficient mice. To further assess the susceptibility of these mice to influenza virus infection, protective efficacy was determined after primary or secondary lethal challenge. We found that MyD88 ؊/؊ and MyD88 ؊/؊ TRIF ؊/؊ mice were more susceptible to primary influenza virus infection than the B6 mice but were fully protected against homologous (H1N1) and heterosubtypic (H5N2) secondary infection when primed with a nonlethal dose of PR8 virus. Taken together, these results show that MyD88 signaling plays an important role for resisting primary influenza virus infection but is dispensable for protection against a secondary lethal challenge.

No abstract

We have generated mutants of Escherichia coli formylmethionine initiator tRNA in which one, two, and all GGG three G-C base pairs in the CCC sequence in the anticodon stem are changed to those found in E. coli elongator methionine tRNA. Overproduction of the mutant tRNAs using M13 recombinants as an expression vector and development of a one-step purification scheme allowed us to purify, characterize, and analyze the function of the mutant tRNAs. After aminoacylation and formylation, the function of mutant formylmethionyl tRNAs was analyzed in an MS2 RNA-directed in vitro protein-synthesizing system, in AUG-dependent ribosomal P site binding, and in initiation factor binding. The mutant tRNAs show progressive loss ofactivity in initiation, the mutant with all three G-C base pairs substituted being the least active. The mutations affect binding to the ribosomal P site. None of the mutations affects binding to initiation factor 2. We also show that there is a progressive increase in accessibility of phosphodiester bonds in the anticodon loop of the three mutants to S1 nuclease, such that the cleavage pattern of the mutant with all three G-C base-pair changes resembles that of elongator tRNAs. These results are consistent with the notion that the contiguous G-C base pairs in the anticodon stem of initiator tRNAs impart on the anticodon loop a unique conformation, which may be important in targeting the initiator tRNA to the ribosomal P site during initiation of protein synthesis.Two classes of methionine tRNAs are present in all organisms. The initiator is used exclusively for initiation of protein synthesis, while the elongator is used for inserting methionine internally in a polypeptide chain (1-3). Because of their special function, initiator tRNAs exhibit unique properties, which distinguish them from elongator tRNAs: (i) initiator tRNAs specifically bind to initiation factor; (ii) initiator tRNAs bind directly to the ribosomal P site, whereas elongator tRNAs are first bound to the A site and later transferred to the P site; (iii) initiator tRNAs do not normally bind to the ribosomal A site and, therefore, do not insert methionine internally. Initiator tRNAs also possess unique sequence and structural features not found in most elongator tRNAs (4). Both prokaryotic and eukaryotic initiator tRNAs contain a run of three Gs and three Cs in the anticodon stem, forming three consecutive G-C pairs. Prokaryotic initiator tRNAs share two additional unique features, the absence of a Watson-Crick base pair at the end of the acceptor stem and the presence of a purine-11-pyrimidine-24 base pair instead of a pyrimidine-11-purine-24 base pair in the dihydrouridine stem (5). The strong conservation of these features suggests that they are related to one or more of the unique properties of initiator tRNAs.We have used oligonucleotide-directed mutagenesis (6, 7) to remove two of the features described above in Escherichia coli tRNAfmet. First, we changed C-1 to T-1 such that the mutant initiator tRNA now has a Watson-Cr...