Engineered FnCas9 for Modifying Genetic Material

The technology discloses engineered variants of Francisella novicida Cas9 (FnCas9) with improved binding kinetics and nucleic acid recognition properties, expanding the enzyme’s potential in both diagnostic and therapeutic settings. These engineered FnCas9 proteins exhibit increased affinity and specificity for target nucleic acids, making them highly suitable for RNA-guided detection systems such as FELUDA (FnCas9 Editor Linked Uniform Detection Assay). Applications include rapid, field-deployable molecular diagnostics for infectious diseases, including COVID-19, as well as genotyping, mutation detection, and SNP discrimination. Beyond diagnostics, the enhanced kinetics may support more precise gene editing and RNA tracking in research and clinical applications. The improved biochemical properties allow for robust signal generation, lower detection limits, and reduced off-target effects, offering advantages over traditional Cas9-based tools in both in vitro and in vivo platforms.

The kinetically enhanced engineered FnCas9 (derived from Francisella novicida Cas9) expands the utility of CRISPR-based systems into a wide range of diagnostic, therapeutic, and research domains due to its improved target binding dynamics, specificity, and signal fidelity. The enhanced enzyme’s core strength lies in its ability to recognize nucleic acid targets with high sensitivity and minimal off-target activity, making it valuable for both nucleic acid detection and genome interaction applications.

1. Molecular Diagnostics

• Nucleic acid detection (DNA or RNA) using FnCas9 as a programmable biosensor with high specificity.
• Foundation of the FELUDA diagnostic platform, allowing rapid, point-of-care testing without the need for complex instrumentation.
• Detection of viral RNA, such as SARS-CoV-2, Influenza, and other pathogens.
• Genotyping, mutation detection, and SNP discrimination, especially in contexts like thalassemia, sickle cell anemia, and cancer-associated mutations.
• Multiplexed diagnostic assays using guide RNA libraries targeting multiple sequences simultaneously.
• Use in paper-based, lateral flow, or microfluidic diagnostic formats.

2. Genome and Transcriptome Engineering

• Use in targeted genome editing, particularly in contexts where lower off-target effects are critical (e.g., in human cells).
• Potential use in allele-specific gene editing, targeting pathogenic variants without affecting wild-type alleles.
• RNA tracking and regulation: catalytically inactivated FnCas9 variants can bind target RNAs for imaging or translational repression.
• Tunable transcriptional regulators when fused with effector domains (e.g., for CRISPRa or CRISPRi systems).

3. Synthetic Biology and Molecular Control Systems

• Integration into synthetic gene circuits that respond to the presence of specific RNA or DNA sequences.
• RNA-triggered control systems in engineered cells, useful for conditional gene expression or biocontainment strategies.
• Can act as a programmable controller in biosensing networks, responding to environmental or cellular signals.

4. Therapeutic Applications

• Development of diagnostics-linked therapeutic systems, where FnCas9 can trigger downstream responses based on detected nucleic acids.
• Potential future use in RNA-guided gene therapy, particularly when adapted to delivery systems (e.g., lipid nanoparticles or AAVs).
• Use in precision medicine to detect patient-specific mutations or pathogens at the point of care.

5. Forensics, Agriculture, and Environmental Monitoring

• Detection of species-specific DNA or RNA for agricultural pathogen surveillance or GMO identification.
• Water and food safety testing, especially where portable, on-site diagnostics are necessary.
• Forensic genotyping applications where rapid, portable, and specific DNA analysis is required.

1. High Specificity and Single-Nucleotide Discrimination

• Engineered FnCas9 has exceptional ability to differentiate single nucleotide polymorphisms (SNPs), outperforming Cas12a/Cas13 which tolerate mismatches in the seed region.
• Superior to wild-type SpCas9 in discriminating mutant vs. wild-type alleles—critical for precision diagnostics and allele-specific detection (e.g., in inherited diseases or cancer mutations).

2. RNA-Programmable, DNA-Targeting with No Collateral Activity

• Unlike Cas12a/Cas13, FnCas9 does not exhibit collateral (trans) cleavage, making it suitable for clean readouts in diagnostics without risk of non-specific degradation.
• Ideal for applications needing high signal-to-noise ratios (e.g., FELUDA platform), where trans cleavage is undesirable.

     3. Kinetic Enhancement Boosts Sensitivity

• Engineered variants show faster and stronger binding kinetics to target sequences, improving reaction speed and detection sensitivity in nucleic acid tests.
• Requires shorter incubation times than unmodified FnCas9 or Cas12-based assays.

4. PAM Flexibility and Broader Targeting Scope

• Modified FnCas9 exhibits relaxed PAM requirements compared to canonical SpCas9 (NGG), expanding the targetable regions of the genome and enhancing applicability in both diagnostics and editing.

5. Compatibility with Multiple Formats

• Performs well in lateral flow, paper-based, and low-resource diagnostic platforms where other systems (e.g., Cas13) may require RNA amplification or complex reaction setups.
• Easier to implement in portable, instrument-free assays than trans-cleaving systems requiring fluorescence-based monitoring.

6. Thermostability and Reaction Robustness

• Engineered FnCas9 variants can retain activity under ambient or elevated temperatures, enabling use in field conditions where other CRISPR enzymes may fail or require cold-chain logistics.

7. Lower Risk of Off-Target Effects

• Improved kinetic control and high sequence specificity reduce off-target binding in both in vitro detection and in vivo editing, making it safer for therapeutic exploration.