The Nobel Prize has been awarded to women 58 times since 1901. Only one woman, Marie Curie, won twice (1903 in Physics and 1911 in Chemistry). The Nobel Prize in Chemistry has only been awarded to women 5 times in the past, most recently in 2018 to Frances Arnold “for the directed evolution of enzymes” who shared the prize with George Smith and Sir Gregory Winter for their discovery of “phage display of peptides and antibodies”. Arnold developed a method to create enzymes or reaction catalysts to produce any number of proteins while Smith and Gregory developed a method to force bacteria to produce the desired proteins such as antibodies developed by Big Pharma to treat a variety of auto-immune disorders including Rheumatoid Arthritis.
This year, Professor Emmanuelle Charpentier and Professor Jennifer Doudna won the 2020 Nobel Prize for their work in the discovery of the CRISPR/Cas9 genome editing technique or otherwise known as the ‘genetic scissors’. This is the first time two women jointly win a Nobel Prize. Using the genetic scissor technique, researchers can literally change the DNA of animals, plants, or microorganisms. It fueled the work being done to edit the human genome to treat genetic disorders and fueled speculation on the future of an engineered super human. Their work is what makes science fiction, like the movie Gattaca, sound much more probable. In fact, Chinese scientist, He Jiankui, was convicted and jailed for three years for violating a government ban when he used the gene editing tool to make human embryos immune to HIV.
Let’s dig deeper to understand what it is they discovered.
How it was discovered: While studying a bacteria called Streptococcus pyogenes which is known to cause fever, strep throat, impetigo, and a few other infections that affect more than 700 million people each year. It’s commonly used because its genome has been sequenced and produces 1700-1900 proteins. Professor Charpentier discovered a molecule called tracrRNA that is part of the CRISPR/Cas systems that protects the bacteria from viruses by cutting their DNA. The work was published in 2011, and soon Charpentier collaborated with Doudna, an experienced biochemist with a deep understanding of RNA to recreate the CRISPR/Cas in the lab with the ability to tell it what and where to cut including DNA from human cells.
“This tool has contributed to many important discoveries in basic research, and plant researchers have been able to develop crops that withstand mould, pests and drought. In medicine, clinical trials of new cancer therapies are underway, and the dream of being able to cure inherited diseases is about to come true. These genetic scissors have taken the life sciences into a new epoch and, in many ways, are bringing the greatest benefit to humankind” - Nobel committee
CRISPR: CRISPR stands for Clustered Regularly Interspaced Short palindromic Repeats. A palindrome is a sequence that reads the same forwards and backwards such as 313. In DNA for example, the DNA sequence ACCTAGGT is palindromic because its nucleotide-by-nucleotide complement is TGGATCCA.
There is still a lot of research on palindrome, but scientists have found them common in the human X and Y chromosomes, and in some instances this sequence allows the Y chromosome to bend on itself to repair any damaged nucleotides or sequences of nucleotides. So it has a purpose and we continue to learn more about them. About 50% of bacteria have an interesting repeating pattern of palindrome repeats with regularly spaced regions that code for something. It wasn’t until recently that we learned that this something can be a piece of an intruder bacteriophage or phage virus DNA. When a bacterium is infected with a bacteriophage with that same DNA, it mobilizes proteins produced by a Cas gene or CRISPR-associated systems to cleave the virus exactly where the DNA matches. This confers a sort of ‘immunity’ from the virus.
CRISPR is the sequence researchers look for, and Cas is the ‘scissors’ that does the work based on the blueprint stored as DNA in the spaces between the palindromic repeats. How do we go from here to building a gene editing system? That’s next.
Cas9: The Cas9 endonuclease (a protein or enzyme that cleaves a nucleotide chain like DNA) was discovered in Streptococcus pyogenes and is made of four molecules including the trans-activating or tracrRNA molecule that Charpentier discovered. Charpentier and Doudna took the Cas9 endonuclease and created a two molecule system by fusing the two RNA molecules (CrRNA and tracrRNA) into a single RNA they called the ‘guide RNA’. This RNA includes the sequence where the Cas9 system should go cut. Therefore, by simply changing the nucleotide sequence inside the guide RNA, they were able to target any part of the DNA for cleavage. To add new DNA, researchers would simply create millions of copies of the new DNA and inject it along with the injection of the reprogrammed Cas9 so once a DNA sequence is cleaved, it copies the new DNA.
Today there are multiple BioTech companies using CRISPR/Cas in a variety of different applications such as Altius which received initial investment from GlaxoSmithKline (NYSE: GSK). To watch a 4 minute video on CRISPR/Cas produced by MIT click here. If you’re even more interested in this space, watch the Netflix documentary Human Nature.