Project description:Argonaute proteins are programmable nucleases that are found in both eukaryotes and prokaryotes and provide defense against invading genetic elements. Although some prokaryotic Argonautes (pAgos) were shown to recognize RNA targets in vitro, the majority of studied pAgos have strict specificity toward DNA, which limits their practical use in RNA-centric applications. Here, we describe a unique pAgo nuclease, KmAgo, from the mesophilic bacterium Kurthia massiliensis that can be programmed with either DNA or RNA guides and can precisely cleave both DNA and RNA targets. KmAgo binds 16-20 nt long 5’-phosphorylated guide molecules with no strict specificity for their sequence and is active in a wide range of temperatures. In bacterial cells, KmAgo is loaded with small DNAs with no obvious sequence preferences suggesting that it can uniformly target genomic sequences. Mismatches between the guide and target sequences greatly affect the efficiency and precision of target cleavage, depending on the mismatch position and the nature of the reacting nucleic acid. Target RNA cleavage by KmAgo depends on the formation of secondary structure indicating that KmAgo can be used for structural probing of RNA. These properties of KmAgo open the way for its use for highly specific nucleic acid detection and cleavage.
Project description:Argonaute proteins are programmable nucleases that are found in both eukaryotes and prokaryotes and provide defense against invading genetic elements. Although some prokaryotic argonautes (pAgos) were shown to recognize RNA targets in vitro, the majority of studied pAgos have strict specificity toward DNA, which limits their practical use in RNA-centric applications. Here, we describe a unique pAgo nuclease, KmAgo, from the mesophilic bacterium Kurthia massiliensis that can be programmed with either DNA or RNA guides and can precisely cleave both DNA and RNA targets. KmAgo binds 16-20 nt long 5'-phosphorylated guide molecules with no strict specificity for their sequence and is active in a wide range of temperatures. In bacterial cells, KmAgo is loaded with small DNAs with no obvious sequence preferences suggesting that it can uniformly target genomic sequences. Mismatches between the guide and target sequences greatly affect the efficiency and precision of target cleavage, depending on the mismatch position and the nature of the reacting nucleic acids. Target RNA cleavage by KmAgo depends on the formation of secondary structure indicating that KmAgo can be used for structural probing of RNA. These properties of KmAgo open the way for its use for highly specific nucleic acid detection and cleavage.
Project description:Argonaute (Ago) proteins are conserved nucleic acid-guided proteins present in all domains of life. Eukaryotic Argonaute proteins (eAgos) are key players in RNA interference pathways and function as RNA-guided RNA endonucleases at physiological temperatures. Although eAgos are considered to evolve from prokaryotic Argonaute proteins (pAgos), previously studied pAgos were unable to catalyze RNA-guided RNA cleavage at physiological temperatures. Here, we describe a distinctive pAgo from mesophilic bacteria Kurthia massiliensis (KmAgo). KmAgo utilizes DNA guides to cleave single-stranded DNA (ssDNA) and RNA targets with high activity. KmAgo also utilizes RNA guides to cleave ssDNA and RNA targets at moderate temperatures. We show that KmAgo can use 5' phosphorylated DNA guides as small as 9-mers to cut ssDNA and RNA, like Clostridium butyricum Ago. Small DNA binding confers remarkable thermostability on KmAgo, and we can suppress the guide-independent plasmid processing activity of empty KmAgo by elevating the DNA guide loaded temperature. Moreover, KmAgo performs programmable cleavage of double-stranded DNA and highly structured RNA at 37°C. Therefore, KmAgo can be regarded as a DNA-guided programmable omnipotent nuclease for cleaving most types of nucleic acids efficiently. This study broadens our understanding of Ago proteins and could expand the pAgo-based DNA and RNA manipulation toolbox.
Project description:CRISPR-Cas systems can be utilized as programmable-spectrum antimicrobials to combat bacterial infections. However, how CRISPR nucleases perform as antimicrobials across target sites and strains remains poorly explored. Here, we address this knowledge gap by systematically interrogating the use of CRISPR antimicrobials against multidrug-resistant and hypervirulent strains of Klebsiella pneumoniae. Comparing different Cas nucleases, we found that AsCas12a exhibited robust targeting across different strains. The elucidated modes of escape from this nuclease varied widely, restraining opportunities to enhance killing. We also encountered individual guide RNAs yielding different extents of clearance across strains. The differences were attributed to improper RNA folding, leading to inefficient DNA cleavage and subsequent repair via homologous recombination. To explore features that could improve targeting across strains, we performed a genome-wide screen in different K. pneumoniae strains that yielded guide design rules and trained an algorithm for predicting guide efficiency. Finally, we showed that Cas12a antimicrobials can be exploited to eliminate K. pneumoniae when encoded in phagemids delivered by T7-like phages. Altogether, our results highlight the importance of evaluating antimicrobial activity of CRISPR antimicrobials across relevant strains and define critical parameters for efficient CRISPR-based targeting.