Indian scientists build breakthrough gene-editor

Sub: Sci

Sec: Biotech

Context:

Researchers at CSIR-IGIB and the L.V. Prasad Eye Institute has engineered new versions of an enzyme that can make CRISPR more precise.

More on the news:

Scientists have developed an enhanced genome-editing system that can modify DNA more precisely and more efficiently than existing CRISPR-based technologies.
CRISPR occurs naturally in some bacteria, as a part of their immune system that limits infections by recognising and destroying viral DNA.

What is CRISPR-Cas9?

CRISPR–Cas9 is a unique technology that enables geneticists and medical researchers to edit parts of the genome by removing, adding or altering sections of the DNA.
It is currently the simplest, most versatile and precise method of genetic manipulation.

How does CRISPR-Cas9 work?

The CRISPR-Cas9 gene editing tool uses a guide-RNA (gRNA) designed to find and bind to a specific part of the target genome.
The gRNA directs an enzyme, Cas9, to the target site, which is followed by a short DNA sequence called protospacer adjacent motif (PAM).
Cas9 recognises and binds to the PAM sequence, and acts as a molecular scissor that snips some damaged DNA.
This automatically triggers the cell’s DNA repair system, which repairs the snipped part to insert the correct DNA sequence.

What is the “off-target” issue of CRISPR-Cas9?

CRISPR-Cas9 system at times recognise and cut parts of the genome other than the intended portion.
Such “off-target” effects are more common when using the SpCas9 enzyme derived from Streptococcus pyogenes bacteria.

What is FnCas9?

FnCas9 protein is a recombinant Cas9 protein derived from a type II-B Francisella novicida Cas9 and expressed in E. coli.
While FnCas9, is highly precise, it has a drawback of being low in efficiency.
Researchers from CSIR-IGIB modified and engineered new versions of FnCas9 by tinkering with amino acids in FnCas9 that recognise and interact with the PAM sequence on the host genome.
Enhanced FnCas9 cut target DNA at a higher rate with increased the binding affinity compared to unmodified FnCas9.
An enhanced FnCas9-based diagnostic could target almost twice the number of changes compared to FnCas9, increasing the scope of detecting more disease-causing genetic changes.