“CRISPR-Cas systems” in bacteria and viruses identify and destroy invading viral sequences. It is bacterial and archaeal immune system for protection against viral infections. In 2012, CRISPR-Cas system was recognised as a הגנום editing tool. Since then, wide range of CRISPR-Cas systems have been developed and have found applications in areas such as in gene therapy, diagnostics, research and crop improvement. However, currently available CRISPR-Cas systems have limited clinical use due to frequent occurrences of off-target editing, unexpected DNA mutations and inheritable problems. Researchers have recently reported a novel CRISPR-Cas system that can target and destroy mRNA and חלבונים associated with different genetic diseases more accurately without off-target impact and inheritable problems. Named Craspase, it is the first CRISPR-Cas system that shows חלבון editing function. It is also the first system that can edit both RNA and חלבון. Because Craspase overcomes many limitations of existing CRISPR-Cas systems, it has potential to revolutionise gene therapy, diagnostics and monitoring, biomedical research, and crop improvement.
“CRISPR-Cas system” is natural immune system of bacteria and archaea against viral infections that identifies, binds and degrades the sequences in the viral gene to protect. It consists of two parts – bacterial RNA transcribed from the viral gene incorporated in the bacterial genome after first infection (called CRISPR, this identifies the target sequences of the invading viral genes) and an associated destroyer חלבון called “CRISPR associated חלבון (Cas)” which binds and degrades the identified sequences in the viral gene to protect the bacteria against viruses.
קריפר stands for “clustered regularly interspaced short palindromic repeats”. It is transcribed bacterial RNA characterised by palindromic repeats.
חזרות פלינדרום (CRISPRs) התגלו לראשונה ברצפים של החיידק in 1987. In 1995, Francisco Mojica observed similar structures in archaea, and it was he who first thought of these as a part of the immune system of bacteria and archaea. In 2008, it was experimentally demonstrated for the first time that the target of the immune system of bacteria and archaea was foreign DNA and not mRNA. The mechanism of identification and degradation viral sequences suggested that such systems could be used as a tool for עריכת גנום. Since its recognition as a genome editing tool in 2012, CRISPR–Cas system has come a very long way as a firmly established standard עריכת גנים system and has found a wide range of applications in biomedicine, agriculture, pharmaceutical industries including in clinical gene therapy1,2.
מגוון רחב של CRISPR-Cas systems are already identified and currently available for monitoring and editing DNA/RNA sequences for research, drug screening, diagnostics and treatments. The current CRISPR/Cas systems are divided into 2 classes (Class 1 and 2) and six types (Type I to XI). Class 1 systems have multiple Cas חלבונים which need to form a functional complex to bind and act on their targets. On the other hand, Class 2 systems have only one large Cas חלבון for binding and degrading target sequences which makes Class 2 systems easier to use. Commonly used Class 2 systems are Cas 9 Type II, Cas13 Type VI, and Cas12 Type V. These systems may have undesired collateral effects I.e., off-target impact and cytotoxicity3,5.
טיפולים גנטיים based on current CRISPR- Cas systems have limited clinical use because of frequent occurrences of off-target editing, unexpected DNA mutations, including big DNA fragment deletions and large DNA structural variants at both on-target and off-target sites that leads to cell deaths and other inheritable problems.
קראספאז (או קספס מונחה CRISPR)
Researchers have recently reported a novel CRISPER-Cas system which is a Class 2 Type III-E Cas7-11 system associated with a caspase-like חלבון hence named קראספאז או קספס מונחה CRISPR 5 (Caspases are cysteine proteases that play key role in apoptosis in breaking down cellular structures). It has potential applications in areas like gene therapy and diagnostics. Craspase is RNA-guided and RNA-targeted and do not get involved with the DNA sequences. It can target and destroy mRNA and חלבונים associated with different genetic diseases more accurately without off-target impact. Thus, elimination of genes associated with diseases is possible by cleavage at mRNA or protein level. Also, when linked with specific enzyme, Craspase can also be used to modify functions of proteins. When its RNase and protease functions are removed, Craspase becomes deactivated (dCraspase). It has no cutting function but binds with RNA and protein sequences. Therefore, dCraspase can be used in diagnostics and imaging to monitor and diagnose diseases or viruses.
Craspase is the first CRISPR-Cas system that shows protein editing function. It is also the first system that can edit both RNA and protein. Its עריכת גנים function comes at minimal off-target effects and no inheritable problems. Hence, Craspase is likely to be safer in clinical use and therapeutics than other currently available CRISPR- Cas systems 4,5.
מכיוון ש-Craspase מתגבר על מגבלות רבות של מערכות CRISPR-Cas קיימות, יש לו פוטנציאל לחולל מהפכה בטיפול גנטי, אבחון וניטור, מחקר ביו-רפואי ושיפור יבול. יש צורך במחקר נוסף כדי לפתח מערכת אספקה אמינה כדי למקד במדויק את הגנים הגורמים למחלות בתאים לפני הוכחת בטיחות ויעילות בניסויים קליניים.
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הפניות:
- Gostimskaya, I. CRISPR–Cas9: היסטוריה של גילויו ושיקולים אתיים של השימוש בו בעריכת הגנום. Biochemistry Moscow 87, 777–788 (2022). https://doi.org/10.1134/S0006297922080090
- צ'או לי ואח' 2022. כלים ומשאבים חישוביים לעריכת גנום CRISPR/Cas. גנומיקה, פרוטאומיקה וביואינפורמטיקה. זמין באינטרנט ב-24 במרץ 2022. DOI: https://doi.org/10.1016/j.gpb.2022.02.006
- van Beljouw, SPB, Sanders, J., Rodríguez-Molina, A. et al. מערכות CRISPR-Cas המכוונות ל-RNA. Nat Rev Microbiol 21, 21–34 (2023). https://doi.org/10.1038/s41579-022-00793-y
- צ'וניי הו ואח' 2022. קראספאז הוא פרוטאז מונחה RNA של CRISPR, מופעל על ידי RNA. מַדָע. 25 באוגוסט 2022. כרך 377, גיליון 6612. עמ' 1278-1285. DOI: https://doi.org/10.1126/science.add5064
- Huo, G., Shepherd, J. & Pan, X. Craspase: עורך גנים כפולים של CRISPR/Cas. Functional & Integrative Genomics 23, 98 (2023). פורסם: 23 במרץ 2023. DOI: https://doi.org/10.1007/s10142-023-01024-0
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