Dear Editor,CRISPR/Cas systems are widespread rna-mediated prokaryotic adaptive immune systems providing protection against invading nucleic acids [1].However,throughout evolution,this host defense system has not resu...
详细信息
Dear Editor,CRISPR/Cas systems are widespread rna-mediated prokaryotic adaptive immune systems providing protection against invading nucleic acids [1].However,throughout evolution,this host defense system has not resulted in the eradication of phages,suggesting that phages have evolved counter strategies to thrive within bacteria despite these mechanisms [2].Thus,both bacterial CRISPR system and phage anti-CRISPR system are part of a continuing evolutionary battle between bacterial host and their bacteriophage invaders.
rna-induced gene silencing has been widely applied as a powerful research tool in drug development due to its sequence-specific degradation of target mrna. Conditional regulation of gene functions with small interferi...
详细信息
The pirna machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves pirna-guided cleavage of transposon-derived transcripts. As many piRN...
详细信息
The pirna machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves pirna-guided cleavage of transposon-derived transcripts. As many pirnas also appear to have the capacity to target diverse mrnas, this raises the intriguing possibility that pirnas may act extensively as sirnas to degrade specific mrnas. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated pirnas with experimentally identified cleaved mrna fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5′ end of putative targeting pirnas. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both pirnas and mrna fragments, features that resemble the pattern of pirna amplification by the 'ping-pong' cycle. Through mapping of MIWI-rna interactions by CLIP-seq and gene expression profiling, we found that many potential pirna-targeted mrnas directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between pirnas and mrna targets and the requirement for both the slicer activity and pirna-loading ability of MIWI in pirna-mediated target repression. Importantly, we demonstrated that proper turnover of certain key pirna targets is essential for sperm formation. Together, these findings reveal the sirna-like function of the pirna machinery in mouse testes and its central requirement for male germ cell development and maturation.
An epidemic of an avian-origin H7N9 influenza virus has recently emerged in China, infecting 134 patients of which 45 have died. This is the first time that an influenza virus harboring an N9 serotype neuraminidase (N...
详细信息
An epidemic of an avian-origin H7N9 influenza virus has recently emerged in China, infecting 134 patients of which 45 have died. This is the first time that an influenza virus harboring an N9 serotype neuraminidase (NA) has been known to infect humans. H7N9 viruses are divergent and at least two distinct NAs and hemagglutinins (HAs) have been found, respectively, from clinical isolates. The prototypes of these viruses are A/Anhui/1/2013 and A/Shanghai/1/2013. NAs from these two viruses are distinct as the A/Shanghai/1/2013 NA has an R294K substitution that can confer NA inhibitor oseltamivir resistance. Oseltamivir is by far the most commonly used anti-influenza drug due to its potency and high bioavailability. In this study, we show that an R294K substitution results in multidrug resistance with extreme oseltamivir resistance (over 100 000-fold) using protein- and virus-based assays. To determine the molecular basis for the inhibitor resistance, we solved high-resolution crystal structures of NAs from A/Anhui/1/2013 N9 (R294-containing) and A/Shanghai/1/2013 N9 (K294-containing). R294K substitution results in an unfavorable E276 conformation for oseltamivir binding, and consequently loss of inhibitor carboxylate interactions, which compromises the binding of all classical NA ligands/inhibitors. Moreover, we found that R294K substitution results in reduced NA catalytic efficiency along with lower viral fitness. This helps to explain why K294 has predominantly been found in clinical cases of H7N9 infection under the selective pressure of oseltamivir treatment and not in the dominant human-infecting viruses. This implies that oseltamivir can still be efficiently used in the treatment of H7N9 infections.
The recently discovered 150-cavity(formed by loop residues 147-152, N2 numbering) adjacent to the enzymatic active site of group 1 influenza A neuraminidase(NA) has introduced a novel target for the design of next-gen...
详细信息
The recently discovered 150-cavity(formed by loop residues 147-152, N2 numbering) adjacent to the enzymatic active site of group 1 influenza A neuraminidase(NA) has introduced a novel target for the design of next-generation NA inhibitors. However, only group 1 NAs, with the exception of the 2009 pandemic H1N1 NA, possess a 150-cavity, and no 150-cavity has been observed in group 2 NAs. The role of the 150-cavity played in enzymatic activity and inhibitor binding is not well understood. Here, we demonstrate for the first time that oseltamivir carboxylate can induce opening of the rigid closed N2 150-loop and provide a novel mechanism for 150-loop movement using molecular dynamics simulations. Our results provide the structural and biophysical basis of the open form of 150-loop and illustrates that the inherent flexibility and the ligand induced flexibility of the 150-loop should be taken into consideration for future drug design.
暂无评论