Progress on the CRISPR genetic techniques improves the chances for their applications

A cryo-electron microscope image of a CRISPR molecule (Image courtesy Liao lab/Harvard Medical School)
A cryo-electron microscope image of a CRISPR molecule (Image courtesy Liao lab/Harvard Medical School)

Two articles published in the journal “Cell” describe two different researches that are connected to one of the DNA modification systems known as CRISPR and especially the one known as CRISPR-Cas3. A team of scientists from Harvard Medical School and Cornell University generated an almost atomic-level snapshot of CRISPR revealing key steps in its operating mechanism. A team of scientists at the University of Texas at Austin and Cornell University took an important step towards the safety of medical applications of the CRISPR systems.

The CRISPR (clustered regularly interspaced short palindromic repeats) acronym refers to prokaryotic DNA segments containing short repeated sequences. The expression CRISPR/Cas refers to a prokaryotic immune system conferring a genetic resistance to foreign elements. The CRISPR/Cas system is used in genetic engineering, in particular using the Cas3 (CRISPR associated protein 3) enzyme, that evolved in bacteria of the species Streptococcus thermophilus as part of their immune system.

There have already been uses of various subtypes of the CRISPR/Cas system ranging from manipulating DNA of bacteria to experimenting genetic therapies for medical purposes. However, there are still doubts and concerns about some aspects of its operating mechanisms. For this reason, various researches were carried out to investigate those mechanisms and seek to improve the safety of genetic modification interventions.

The Harvard and Cornell team used the cryo-electron microscopy (cryo-EM) technique, a transmission electronic microscopy technique (TEM) technique that offers an almost atomic resolution. It’s also used for the study of highly symmetrical proteins and can be applied to DNA segments such as CRISPR.

This technique was coupled with other biochemical techniques to reconstruct CRISPR Cascade, the protein complex to capture DNA pieces and for the Cas3 enzyme to cut DNA, in various operating states. In this way it was possible to reconstruct the “cut & paste” process performed by Cas3 at a resolution of 3.3 angstrom, about 3 times the diameter of a carbon atom.

The team at University of Texas at Austin and Cornell developed a way to quickly test a CRISPR molecule in the whole person’s genome to verify its possibility to interact with DNA segments different than their target. Called possibilità (Chip Hybridized Affinity Mapping Platform), this test focuses on a genetic sequencing technique already widely used in the field of research and also in the medical field.

The researchers adapted that technique to provide details on the interaction of CRISPR with the genome. In essence, this is an extension of the use of an existing technique that sometimes provided surprising results. For example, the Cascade molecule pays less attention to every third letter of a DNA sequence than the others, a feature due to its origin as part of an immune system.

Progress such as those obtained through these two researches will improve the application of CRISPR techniques. The experimentation in the field of genetic engineering is still in its initial stages and rightly there’s a lot of cautiousness but a greater understanding of its mechanisms of operation and above all a greater safety will lead to improvements in its medical applications.

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