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Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) in association with CRISPR-associated (Cas) proteins constitutes a formidable defense system against mobile genetic elements in prokaryotes. In type I-C, the ribonucleoprotein surveillance complex comprises only three Cas proteins, namely, Cas5d, Csd1 and Csd2. Unlike type I-E that uses Cse3/CasE for metal-independent CRISPR RNA maturation, type I-C that lacks this deputes Cas5d to process the pre-crRNA. Here, we report the promiscuous DNase activity of Cas5d in presence of divalent metals. Remarkably, the active site that renders RNA hydrolysis may be tuned by metal to act on DNA substrates too. Further, the realization that Csd1 is a fusion of its functional homolog Cse1/CasA and Cse2/CasB forecasts that the stoichiometry of the constituents of the surveillance complex in type I-C may differ from type I-E. Although Csd2 seems to be inert, Csd1 too exhibits RNase and metal-dependent DNase activity. Thus, in addition to their proposed functions, the DNase activity of Cas5d and Csd1 may also enable them to be co-opted in adaptation and interference stages of CRISPR immunity wherein interaction with DNA substrates is involved. 相似文献
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During protein synthesis, tRNA serves as the intermediary between cognate amino acids and their corresponding RNA trinucleotide codons. Aminoacyl-tRNA is also a biosynthetic precursor and amino acid donor for other macromolecules. AA-tRNAs allow transformations of acidic amino acids into their amide-containing counterparts, and seryl-tRNASer donates serine for antibiotic synthesis. Aminoacyl-tRNA is also used to cross-link peptidoglycan, to lysinylate the lipid bilayer, and to allow proteolytic turnover via the N-end rule. These alternative functions may signal the use of RNA in early evolution as both a biological scaffold and a catalyst to achieve a wide variety of chemical transformations. 相似文献
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Neeraj Maheshwari Satish Kantipudi Anand Maheshwari Kashika Arora Vandana Neha Kwatra Girish Sahni 《PloS one》2016,11(3)
Streptokinase (SK) is a potent clot dissolver but lacks fibrin clot specificity as it activates human plasminogen (HPG) into human plasmin (HPN) throughout the system leading to increased risk of bleeding. Another major drawback associated with all thrombolytics, including tissue plasminogen activator, is the generation of transient thrombin and release of clot-bound thrombin that promotes reformation of clots. In order to obtain anti-thrombotic as well as clot-specificity properties in SK, cDNAs encoding the EGF 4,5,6 domains of human thrombomodulin were fused with that of streptokinase, either at its N- or C-termini, and expressed these in Pichia pastoris followed by purification and structural-functional characterization, including plasminogen activation, thrombin inhibition, and Protein C activation characteristics. Interestingly, the N-terminal EGF fusion construct (EGF-SK) showed plasmin-mediated plasminogen activation, whereas the C-terminal (SK-EGF) fusion construct exhibited ‘spontaneous’ plasminogen activation which is quite similar to SK i.e. direct activation of systemic HPG in absence of free HPN. Since HPN is normally absent in free circulation due to rapid serpin-based inactivation (such as alpha-2-antiplasmin and alpha-2-Macroglobin), but selectively present in clots, a plasmin-dependent mode of HPG activation is expected to lead to a desirable fibrin clot-specific response by the thrombolytic. Both the N- and C-terminal fusion constructs showed strong thrombin inhibition and Protein C activation properties as well, and significantly prevented re-occlusion in a specially designed assay. The EGF-SK construct exhibited fibrin clot dissolution properties with much-lowered levels of fibrinogenolysis, suggesting unmistakable promise in clot dissolver therapy with reduced hemorrhage and re-occlusion risks. 相似文献
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R. K. Anand 《BMJ (Clinical research ed.)》1996,312(7046):1556-1557