scholarly journals Engineered dual selection for directed evolution of SpCas9 PAM specificity

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gregory W. Goldberg ◽  
Jeffrey M. Spencer ◽  
David O. Giganti ◽  
Brendan R. Camellato ◽  
Neta Agmon ◽  
...  
Keyword(s):  
Directed Evolution ◽  
Negative Selection ◽  
Selection Procedures ◽  
Guide Rna ◽  
Dna Targeting ◽  
Protospacer Adjacent Motif ◽  
Target Dna ◽  
Selection For ◽  
Reduced Activity

AbstractThe widely used Streptococcus pyogenes Cas9 (SpCas9) nuclease derives its DNA targeting specificity from protein-DNA contacts with protospacer adjacent motif (PAM) sequences, in addition to base-pairing interactions between its guide RNA and target DNA. Previous reports have established that the PAM specificity of SpCas9 can be altered via positive selection procedures for directed evolution or other protein engineering strategies. Here we exploit in vivo directed evolution systems that incorporate simultaneous positive and negative selection to evolve SpCas9 variants with commensurate or improved activity on NAG PAMs relative to wild type and reduced activity on NGG PAMs, particularly YGG PAMs. We also show that the PAM preferences of available evolutionary intermediates effectively determine whether similar counterselection PAMs elicit different selection stringencies, and demonstrate that negative selection can be specifically increased in a yeast selection system through the fusion of compensatory zinc fingers to SpCas9.

scholarly journals Programming PAM antennae for efficient CRISPR-Cas9 DNA editing

2020 ◽  
Vol 6 (19) ◽  
pp. eaay9948
Author(s):  
Fei Wang ◽  
Yaya Hao ◽  
Qian Li ◽  
Jiang Li ◽  
Honglu Zhang ◽  
...  
Keyword(s):  
Genome Editing ◽  
Single Molecule ◽  
Dna Cleavage ◽  
Super Resolution ◽  
Single Molecule Level ◽  
Guide Rna ◽  
Guide Rnas ◽  
Protospacer Adjacent Motif ◽  
Target Dna

Bacterial CRISPR-Cas9 nucleases have been repurposed as powerful genome editing tools. Whereas engineering guide RNAs or Cas nucleases have proven to improve the efficiency of CRISPR editing, modulation of protospacer-adjacent motif (PAM), indispensable for CRISPR, has been less explored. Here, we develop a DNA origami–based platform to program a PAM antenna microenvironment and address its performance at the single-molecule level with submolecular resolution. To mimic spatially controlled in vivo PAM distribution as may occur in chromatin, we investigate the effect of PAM antennae surrounding target DNA. We find that PAM antennae effectively sensitize the DNA cleavage by recruiting Cas9 molecules. Super-resolution tracking of single single-guide RNA/Cas9s reveals localized translocation of Cas9 among spatially proximal PAMs. We find that the introduction of the PAM antennae effectively modulates the microenvironment for enhanced target cleavage (up to ~50%). These results provide insight into factors that promote more efficient genome editing.

scholarly journals Enhancement of target specificity of CRISPR–Cas12a by using a chimeric DNA–RNA guide

2020 ◽  
Vol 48 (15) ◽  
pp. 8601-8616 ◽  
Author(s):  
Hanseop Kim ◽  
Wi-jae Lee ◽  
Yeounsun Oh ◽  
Seung-Hun Kang ◽  
Junho K Hur ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Genome Engineering ◽  
Target Genes ◽  
Target Sequence ◽  
Energy Potential ◽  
Guide Rna ◽  
Sequence Recognition ◽  
Protospacer Adjacent Motif ◽  
Effective Manner ◽  
Target Dna

Abstract The CRISPR–Cas9 system is widely used for target-specific genome engineering. CRISPR–Cas12a (Cpf1) is one of the CRISPR effectors that controls target genes by recognizing thymine-rich protospacer adjacent motif (PAM) sequences. Cas12a has a higher sensitivity to mismatches in the guide RNA than does Cas9; therefore, off-target sequence recognition and cleavage are lower. However, it tolerates mismatches in regions distant from the PAM sequence (TTTN or TTN) in the protospacer, and off-target cleavage issues may become more problematic when Cas12a activity is improved for therapeutic purposes. Therefore, we investigated off-target cleavage by Cas12a and modified the Cas12a (cr)RNA to address the off-target cleavage issue. We developed a CRISPR–Cas12a that can induce mutations in target DNA sequences in a highly specific and effective manner by partially substituting the (cr)RNA with DNA to change the energy potential of base pairing to the target DNA. A model to explain how chimeric (cr)RNA guided CRISPR–Cas12a and SpCas9 nickase effectively work in the intracellular genome is suggested. Chimeric guide-based CRISPR- Cas12a genome editing with reduced off-target cleavage, and the resultant, increased safety has potential for therapeutic applications in incurable diseases caused by genetic mutations.

scholarly journals A method to convert mRNA into a gRNA library for CRISPR/Cas9 editing of any organism

2016 ◽  
Vol 2 (8) ◽  
pp. e1600699 ◽  
Author(s):  
Hiroshi Arakawa
Keyword(s):  
Dna Sequences ◽  
Genetic Screening ◽  
Restriction Enzymes ◽  
Mrna Sequence ◽  
Complementary Sequence ◽  
Complementary Dna ◽  
Random Primer ◽  
Guide Rna ◽  
Protospacer Adjacent Motif ◽  
Target Dna

The clustered regularly interspersed palindromic repeats (CRISPR)/Cas9 (CRISPR-associated protein 9) system is a powerful tool for genome editing that can be used to construct a guide RNA (gRNA) library for genetic screening. For gRNA design, one must know the sequence of the 20-mer flanking the protospacer adjacent motif (PAM), which seriously impedes experimentally making gRNA. I describe a method to construct a gRNA library via molecular biology techniques without relying on bioinformatics. Briefly, one synthesizes complementary DNA from the mRNA sequence using a semi-random primer containing a PAM complementary sequence and then cuts out the 20-mer adjacent to the PAM using type IIS and type III restriction enzymes to create a gRNA library. The described approach does not require prior knowledge about the target DNA sequences, making it applicable to any species.

scholarly journals Quantification of the affinities of CRISPR–Cas9 nucleases for cognate protospacer adjacent motif (PAM) sequences

2020 ◽  
Vol 295 (19) ◽  
pp. 6509-6517 ◽  
Author(s):  
Vladimir Mekler ◽  
Konstantin Kuznedelov ◽  
Konstantin Severinov
Keyword(s):  
Genome Editing ◽  
Target Location ◽  
Dna Probes ◽  
Target Sequence ◽  
Francisella Novicida ◽  
Guide Rna ◽  
Guide Rnas ◽  
Cas9 Nuclease ◽  
Protospacer Adjacent Motif ◽  
Target Dna

The CRISPR/Cas9 nucleases have been widely applied for genome editing in various organisms. Cas9 nucleases complexed with a guide RNA (Cas9–gRNA) find their targets by scanning and interrogating the genomic DNA for sequences complementary to the gRNA. Recognition of the DNA target sequence requires a short protospacer adjacent motif (PAM) located outside this sequence. Given that the efficiency of target location may depend on the strength of interactions that promote target recognition, here we sought to compare affinities of different Cas9 nucleases for their cognate PAM sequences. To this end, we measured affinities of Cas9 nucleases from Streptococcus pyogenes, Staphylococcus aureus, and Francisella novicida complexed with guide RNAs (gRNAs) (SpCas9–gRNA, SaCas9–gRNA, and FnCas9–gRNA, respectively) and of three engineered SpCas9–gRNA variants with altered PAM specificities for short, PAM-containing DNA probes. We used a “beacon” assay that measures the relative affinities of DNA probes by determining their ability to competitively affect the rate of Cas9–gRNA binding to fluorescently labeled target DNA derivatives called “Cas9 beacons.” We observed significant differences in the affinities for cognate PAM sequences among the studied Cas9 enzymes. The relative affinities of SpCas9–gRNA and its engineered variants for canonical and suboptimal PAMs correlated with previous findings on the efficiency of these PAM sequences in genome editing. These findings suggest that high affinity of a Cas9 nuclease for its cognate PAM promotes higher genome-editing efficiency.

scholarly journals CrisPam: SNP-derived PAM analysis web tool and human pathogenic SNPs database for CRISPR allele-specific targeting

2019 ◽  
Author(s):  
Roy Rabinowitz ◽  
Roy Darnell ◽  
Daniel Offen
Keyword(s):  
Dna Cleavage ◽  
Variant Allele ◽  
Nucleotide Polymorphisms ◽  
Single Nucleotide ◽  
Guide Rna ◽  
Dna Targeting ◽  
Specific Targeting ◽  
Novel Technology ◽  
Protospacer Adjacent Motif ◽  
Allele Specific

Abstract Background CRISPR is a promising novel technology for treating genetic conditions. Therefore, it is essential to further develop and promote treatment’s safety and specificity. While the guide-RNA offers position-specific DNA targeting, it may tolerate small changes such as single-nucleotide polymorphisms (SNPs). To that end, an allele-specific targeting approach is in need for future treatments of heterozygous patients, suffering from genetic conditions caused by a SNP. The SNP-derived PAM approach allows highly allele-specific DNA cleavage by incorporating a protospacer adjacent motif (PAM) sequence only at the target allele. Description Here we present CrisPam, a tool that detects SNP-derived PAMs for allele-specific targeting by the CRISPR/Cas system. The algorithm scans the generation of each reported PAM for a given DNA sequence and its variations. A successful result is such that at least one PAM is generated by a SNP. Thus, the PAM shall be part of the variant allele only and the Cas protein will therefore be able to exclusively bind the variant allele for gene-editing, while the wildtype allele remains unchanged. Conclusion CrisPam is available online for researchers and also offers access to the CrisPamDB, a database that contains the CrisPam analysis for any reported pathogenic SNP in humans.

scholarly journals Cas12a trans-cleavage can be modulated in vitro and is active on ssDNA, dsDNA, and RNA

2019 ◽  
Author(s):  
Ryan T. Fuchs ◽  
Jennifer Curcuru ◽  
Megumu Mabuchi ◽  
Paul Yourik ◽  
G. Brett Robb
Keyword(s):  
Dna Sequences ◽  
Nuclease Activity ◽  
Target Sequence ◽  
Sequence Composition ◽  
Guide Rna ◽  
Dna Targeting ◽  
Single Turnover ◽  
Target Dna ◽  
Buffer Composition

ABSTRACTCRISPR-Cas12a (Cpf1) are RNA-guided nuclease effectors of acquired immune response that act in their native organisms by cleaving targeted DNA sequences. Like CRISPR-Cas9 RNA-guided DNA targeting enzymes, Cas12a orthologs have been repurposed for genome editing in non-native organisms and for DNA manipulationin vitro. Recent studies have shown that activation of Cas12a via guide RNA-target DNA pairing causes multiple turnover, non-specific ssDNA degradation intrans, after single turnover on-target cleavage incis. We find that the non-specifictransnuclease activity affects RNA and dsDNA in addition to ssDNA, an activity made more evident by adjustment of reaction buffer composition. The magnitude of thetransnuclease activity varies depending on features of the guide RNA being used, specifically target sequence composition and length. We also find that the magnitude oftransnuclease activity varies between the three most well-studied Cas12a orthologs and that the Cas12a fromLachnospiraceaebacterium ND2006 appears to be the most active.

scholarly journals CRISPR-Cas9 bends and twists DNA to read its sequence

2021 ◽  
Author(s):  
Joshua C. Cofsky ◽  
Katarzyna M. Soczek ◽  
Gavin J. Knott ◽  
Eva Nogales ◽  
Jennifer A. Doudna
Keyword(s):  
Genome Editing ◽  
Target Sequence ◽  
Base Flipping ◽  
Base Pairs ◽  
Guide Rna ◽  
Target Capture ◽  
Dna Base ◽  
Protospacer Adjacent Motif ◽  
Target Dna ◽  
Dna Base Pairs

In bacterial defense and genome editing applications, the CRISPR-associated protein Cas9 searches millions of DNA base pairs to locate a 20-nucleotide, guide-RNA-complementary target sequence that abuts a protospacer-adjacent motif (PAM)1. Target capture requires Cas9 to unwind DNA at candidate sequences using an unknown ATP-independent mechanism2,3. Here we show that Cas9 sharply bends and undertwists DNA at each PAM, thereby flipping DNA nucleotides out of the duplex and toward the guide RNA for sequence interrogation. Cryo-electron-microscopy (EM) structures of Cas9:RNA:DNA complexes trapped at different states of the interrogation pathway, together with solution conformational probing, reveal that global protein rearrangement accompanies formation of an unstacked DNA hinge. Bend-induced base flipping explains how Cas9 “reads” snippets of DNA to locate target sites within a vast excess of non-target DNA, a process crucial to both bacterial antiviral immunity and genome editing. This mechanism establishes a physical solution to the problem of complementarity-guided DNA search and shows how interrogation speed and local DNA geometry may influence genome editing efficiency.

scholarly journals In Vivo Evolution of Butane Oxidation by Terminal Alkane Hydroxylases AlkB and CYP153A6

2008 ◽  
Vol 75 (2) ◽  
pp. 337-344 ◽  
Author(s):  
Daniel J. Koch ◽  
Mike M. Chen ◽  
Jan B. van Beilen ◽  
Frances H. Arnold
Keyword(s):  
Directed Evolution ◽  
Chain Length ◽  
Carbon Sources ◽  
Evolution System ◽  
Alkane Hydroxylase ◽  
Medium Chain ◽  
Medium Chain Length ◽  
Selection For ◽  
Alkane Hydroxylases

ABSTRACT Enzymes of the AlkB and CYP153 families catalyze the first step in the catabolism of medium-chain-length alkanes, selective oxidation of the alkane to the 1-alkanol, and enable their host organisms to utilize alkanes as carbon sources. Small, gaseous alkanes, however, are converted to alkanols by evolutionarily unrelated methane monooxygenases. Propane and butane can be oxidized by CYP enzymes engineered in the laboratory, but these produce predominantly the 2-alkanols. Here we report the in vivo-directed evolution of two medium-chain-length terminal alkane hydroxylases, the integral membrane di-iron enzyme AlkB from Pseudomonas putida GPo1 and the class II-type soluble CYP153A6 from Mycobacterium sp. strain HXN-1500, to enhance their activity on small alkanes. We established a P. putida evolution system that enables selection for terminal alkane hydroxylase activity and used it to select propane- and butane-oxidizing enzymes based on enhanced growth complementation of an adapted P. putida GPo12(pGEc47ΔB) strain. The resulting enzymes exhibited higher rates of 1-butanol production from butane and maintained their preference for terminal hydroxylation. This in vivo evolution system could be useful for directed evolution of enzymes that function efficiently to hydroxylate small alkanes in engineered hosts.

scholarly journals CRISPR-Cas9 bends and twists DNA to read its sequence

2021 ◽  
Author(s):  
Jennifer Doudna ◽  
Joshua Cofsky ◽  
Katarzyna Soczek ◽  
Gavin Knott ◽  
Eva Nogales
Keyword(s):  
Genome Editing ◽  
Target Sequence ◽  
Base Flipping ◽  
Base Pairs ◽  
Guide Rna ◽  
Target Capture ◽  
Dna Base ◽  
Protospacer Adjacent Motif ◽  
Target Dna ◽  
Dna Base Pairs

Abstract In bacterial defense and genome editing applications, the CRISPR-associated protein Cas9 searches millions of DNA base pairs to locate a 20-nucleotide, guide-RNA-complementary target sequence that abuts a protospacer-adjacent motif (PAM). Target capture requires Cas9 to unwind DNA at candidate sequences using an unknown ATP-independent mechanism. Here we show that Cas9 sharply bends and undertwists DNA at each PAM, thereby flipping DNA nucleotides out of the duplex and toward the guide RNA for sequence interrogation. Cryo-electron-microscopy (EM) structures of Cas9:RNA:DNA complexes trapped at different states of the interrogation pathway, together with solution conformational probing, reveal that global protein rearrangement accompanies formation of an unstacked DNA hinge. Bend-induced base flipping explains how Cas9 “reads” snippets of DNA to locate target sites within a vast excess of non-target DNA, a process crucial to both bacterial antiviral immunity and genome editing. This mechanism establishes a physical solution to the problem of complementarity-guided DNA search and shows how interrogation speed and local DNA geometry may influence genome editing efficiency.

scholarly journals Kinetic basis for DNA target specificity of CRISPR-Cas12a

2018 ◽  
Author(s):  
Isabel Strohkendl ◽  
Fatema A. Saifuddin ◽  
James R. Rybarski ◽  
Ilya J. Finkelstein ◽  
Rick Russell
Keyword(s):  
Dna Cleavage ◽  
Target Sequence ◽  
Seed Region ◽  
Target Specificity ◽  
Loop Formation ◽  
Guide Rna ◽  
Dna Targeting ◽  
Cas9 Nuclease ◽  
Protospacer Adjacent Motif ◽  
Late Transition

SUMMARYClass II CRISPR-Cas nucleases are programmable via a single guide RNA, enabling genome editing applications in nearly all organisms. However, DNA cleavage at off-target sites that resemble the target sequence is a pervasive problem that remains poorly understood mechanistically. Here, we use quantitative kinetics to dissect the reaction steps of DNA targeting by Acidaminococcus sp Cas12a (also known as Cpf1). We show that Cas12a binds DNA tightly in two kinetically-separable steps. Protospacer-adjacent motif (PAM) recognition is followed by rate-limiting R-loop propagation, leading to inevitable DNA cleavage of both strands. Despite the functionally irreversible binding, Cas12a discriminates strongly against mismatches along most of the DNA target sequence, implying substantial reversibility during R-loop formation –a late transition state– and the absence of a ‘seed’ region. Our results provide a quantitative underpinning for the DNA cleavage patterns measured in vivo and observations of greater reported target specificity of Cas12a than the Cas9 nuclease.

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