Nav: Home

Unveiling the role of selenocysteine, the mysterious 21st amino acid

March 11, 2019

All the cells of an organism contain a copy of DNA in their nucleus. In order to implement the instructions it contains, this DNA must be copied into an RNA molecule, which reaches the ribosomes, which in turn read this information and synthesise proteins. The codons, animo acid triplets that form proteins and are the markers the ribosomes need to know how to produce each protein, are key in this transition process. There exist a total of 61 codons that code for 20 amino acids, and three codons that act as stop signals in the translation process.

Nevertheless, certain organisms use an extra amino acid, selenocysteine, dubbed the 21st amino acid, which lacks its own codon and uses a stop codon after modifying it. For this purpose, it avails itself of complex machinery, with specific enzymes and RNA; this process can prove to be very costly for the cell. But why? What function does this amino acid have in proteins? Why is it present in humans and in the other vertebrates whereas, on the other hand, other species have lost it? Now, researchers from the Centre for Genomic Regulation (CRG) in Barcelona, part of the Barcelona Institute of Science and Technology, in collaboration with CRG Alumni Marco Mariotti and Vadim N. Gladyshev, from the Harvard Medical School (USA), and Gustavo Salinas from the University of the Republic in Uruguay, have shed some light on these questions.

"In previous studies, we discovered that the machinery of selenocysteine had been lost many times in the course of evolution and we began to take an interest in why it disappears so easily in some groups but not in others", explains the ICREA Research Professor Toni Gabaldón, head of the CRG's Comparative Genomics group.

The fungi were the only organism kingdom in which a species with selenocysteine had never been found, and the researchers decided to focus on them, leveraging the recent publication of a thousand fungi genomes in public-access databases. On analysing them, they discovered, as they reported in the article published in Nature Microbiology, that nine of the 1,000 species actually did have this amino acid.

"It came as a surprise to us, because no fungi were believed to have selenocysteine", says Gabaldón, which explains why the nine species they discovered that did have it belong to relatively unsequenced groups of fungi that "diverged at an early stage in the evolution of fungi, which means that we will probably find more cases of selenocysteine when more genomes of these groups are sequenced".

The ancestor of the fungi that they have identified with this amino acid also had it. Certain lineages have retained it, whereas others have lost it, which could also be the case in other organisms. "The question that remains to be answered is why it is lost in some organisms whereas in others these genes are essential", says Gabaldón. "Understanding why selenocysteine is important in fungi and other branches of the tree of life may help us to understand why it is so important to our species and to define what makes selenium essential to human health", he concludes.

Center for Genomic Regulation

Related Evolution Articles:

Insect evolution: Insect evolution
Scientists at Ludwig-Maximilians-Universitaet (LMU) in Munich have shown that the incidence of midge and fly larvae in amber is far higher than previously thought.
Evolution of aesthetic dentistry
One of the main goals of dental treatment is to mimic teeth and design smiles in the most natural and aesthetic manner, based on the individual and specific needs of the patient.
An evolution in the understanding of evolution
In an open-source research paper, a UVA Engineering professor and her former Ph.D. student share a new, more accurate method for modeling evolutionary change.
Chemical evolution -- One-pot wonder
Before life, there was RNA: Scientists at Ludwig-Maximilians-Universitaet (LMU) in Munich show how the four different letters of this genetic alphabet could be created from simple precursor molecules on early Earth -- under the same environmental conditions.
Catching evolution in the act
Researchers have produced some of the first evidence that shows that artificial selection and natural selection act on the same genes, a hypothesis predicted by Charles Darwin in 1859.
Guppies teach us why evolution happens
New study on guppies shows that animals evolve in response the the environment they create in the absence of predators, rather than in response to the risk of being eaten.
Undercover evolution
Our individuality is encrypted in our DNA, but it is deeper than expected.
Evolution designed by parasites
In 'Invisible Designers: Brain Evolution Through the Lens of Parasite Manipulation,' published in the September 2019 issue of The Quarterly Review of Biology, Marco Del Giudice explores an overlooked aspect of the relationship between parasites and their hosts by systematically discussing the ways in which parasitic behavior manipulation may encourage the evolution of mechanisms in the host's nervous and endocrine systems.
Tracing the evolution of vision
The function of the visual photopigment rhodopsin and its action in the retina to facilitate vision is well understood.
Directed evolution comes to plants
Accelerating plant evolution with CRISPR paves the way for breeders to engineer new crop varieties.
More Evolution News and Evolution Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at