It is established that for CRISPR-Cas9 applications guide RNAs with 17–20 bp long spacer sequences are optimal for accurate target binding and cleavage. In this work we perform cell-free CRISPRa (CRISPR activation) and CRISPRi (CRISPR inhibition) experiments to demonstrate the existence of a complex dependence of CRISPR-Cas9 binding as a function of the spacer length and complementarity. Our results show that significantly truncated or mismatched spacer sequences can form stronger guide–target bonds than the conventional 17–20 bp long spacers. To explain this phenomenon, we take into consideration previous structural and single-molecule CRISPR-Cas9 experiments and develop a novel thermodynamic model of CRISPR-Cas9 target recognition.
CRISPR-based gene drives offer promising means to reduce the burden of pests and vector-borne diseases. These techniques consist of releasing genetically modified organisms carrying CRISPR-Cas nucleases designed to bias their inheritance and rapidly propagate desired modifications. Gene drives can be intended to reduce reproductive capacity of harmful insects or spread anti-pathogen effectors through wild populations, even when these confer fitness disadvantages. Technologies capable of halting the spread of gene drives may prove highly valuable in controlling, counteracting, and even reverting their effect on individual organisms as well as entire populations. Here we show engineering and testing of a genetic approach, based on the germline expression of a phage-derived anti-CRISPR protein (AcrIIA4), able to inactivate CRISPR-based gene drives and restore their inheritance to Mendelian rates in the malaria vector Anopheles gambiae. Modeling predictions and cage testing show that a single release of male mosquitoes carrying the AcrIIA4 protein can block the spread of a highly effective suppressive gene drive preventing population collapse of caged malaria mosquitoes.
This short video illustrates how the myTXTL system utilizes the power of cell-free expression for high throughput discovery in protein engineering.
Cell-free expression systems have drawn increasing attention as a tool to achieve complex biological functions outside of the cell. Several applications of the technology involve the delivery of functionality to challenging environments, such as ﬁeldforward diagnostics or point-of-need manufacturing of pharmaceuticals. To achieve these goals, cell-free reaction components are preserved using encapsulation or lyophilization methods, both of which often involve an embedding of components in porous matrices like paper or hydrogels. Previous work has shown a range of impacts of porous materials on cell-free expression reactions. Here, we explored a panel of 32 paperlike materials and 5 hydrogel materials for the impact on reaction performance. The screen included a tolerance to lyophilization for reaction systems based on both cell lysates and puriﬁed expression components. For paperlike materials, we found that (1) materials based on synthetic polymers were mostly incompatible with cell-free expression, (2) lysate-based reactions were largely insensitive to the matrix for cellulosic and microﬁber materials, and (3) puriﬁed systems had an improved performance when lyophilized in cellulosic but not microﬁber matrices. The impact of hydrogel materials ranged from completely inhibitory to a slight enhancement. The exploration of modulating the rehydration volume of lyophilized reactions yielded reaction speed increases using an enzymatic colorimetric reporter of up to twofold with an optimal ratio of 2:1 lyophilized reaction to rehydration volume for the lysate system and 1.5:1 for the puriﬁed system. The eﬀect was independent of the matrices assessed. Testing with a ﬂuorescent nonenzymatic reporter and no matrix showed similar improvements in both yields and reaction speeds for the lysate system and yields but not reaction speeds for the puriﬁed system. We ﬁnally used these observations to show an improved performance of two sensors that span reaction types, matrix, and reporters. In total, these results should enhance eﬀorts to develop ﬁeld-forward applications of cell-free expression systems.
Cell-free protein expression (CFPS) from E. coli cell lysate is an established chemical biology technique. Common eﬀorts to improve synthesis capacity, such as strain engineering and process improvements, have overlooked the opportunity to increase productivity by reducing the dependence on limited, dissolved oxygen. Here we demonstrate conditioning E. coli cells for anaerobic respiration which increases the initial protein expression rate up to 4-fold and increases titer by 50% as compared to traditional aerobic cell lysate when using sfGFP as a reporter protein in CFPS reactions run at atmospheric conditions. This enhancement is even more signiﬁcant when run in an oxygen-depleted environment, where anaerobic respiration preconditioned cells increase yield when supplemented with nitrite as a terminal electron acceptor (TEA). Furthermore, we test knockout mutants to determine key proteins responsible for enhancing the anaerobically prepared CFPS lysate. Further improvements could be made in preconditioning cells by increasing expression levels of critical pathway enzymes or by screening other TEA.
Safety Data Sheet (SDS) for myTXTL Plasmid and Linear DNA, HP-Grade. US version
Safety Data Sheet (SDS) for myTXTL Plasmid and Linear DNA, HP-Grade. EU version
CRISPR technologies increasingly require spatiotemporal and dosage control of nuclease activity. One promising strategy involves linking nuclease activity to a cell’s transcriptional state by engineering guide RNAs (gRNAs) to function only after complexing with a ‘trigger’ RNA. However, standard gRNA switch designs do not allow independent selection of trigger and guide sequences, limiting gRNA switch application. Here, we demonstrate the modular design of Cas12a gRNA switches that decouples selection of these sequences. The 5 end of the Cas12a gRNA is fused to two distinct and nonoverlapping domains: one base pairs with the gRNA repeat, blocking formation of a hairpin required for Cas12a recognition; the other hybridizes to the RNA trigger, stimulating refolding of the gRNA repeat and subsequent gRNA-dependent Cas12a activity. Using a cell-free transcription-translation system and Escherichia coli, we show that designed gRNA switches can respond to different triggers and target different DNA sequences. Modulating the length and composition of the sensory domain altered gRNA switch performance. Finally, gRNA switches could be designed to sense endogenous RNAs expressed only under speciﬁc growth conditions, rendering Cas12a targeting activity dependent on cellular metabolism and stress. Our design framework thus further enables tethering of CRISPR activities to cellular states.
We study the liquid-liquid phase separation (LLPS) of a cell-free transcription-translation (TXTL) system. When the TXTL reaction, composed of a large amount of proteins, is concentrated, the uniformly mixed state becomes unstable and membrane-less droplets form spontaneously. This LLPS droplet formation can be induced when the TXTL reaction is enclosed in water-in-oil emulsion droplets in which water evaporates (dehydration) from the surface. As the emulsion droplets shrink, smaller LLPS droplets appear inside the emulsion droplets and coalesce into phase-separated domains that partition the location of proteins. We show that the LLPS in the emulsion droplets can be accelerated by interfacial drift in the outer oil phase. This further provides an experimental platform for studying the interplay between biological reactions and intracellular phase separation.
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