sciencetech-blog

comments

Scientists have mimicked natural evolution in a test tube to come up with an enzyme that may have been crucial to the origins of life on Earth.

The enzyme is called ribozyme, and it is made from ribonucleic acid (RNA) - a molecule that is already known as essential for creating forms of life.

And, the enzyme not only reveals clues about how life may have begun, and subsequently evolved - the breakthrough could provide a tool for evolving molecules in the future. 

Origins of life explained? Scientists have mimicked natural evolution in a test tube to come up with an enzyme that may have been crucial to the origin of life on Earth. It's called ribozyme and is made from ribonucleic acid (RNA - illustrated) - a molecule that is essential for all known forms of life

Scientists at The Scripps Research Institute in San Diego, California, created the enzyme made from RNA.

Modern DNA-based life forms appear to have evolved from a simpler 'RNA world', in which molecules self-replicated and evolved.

The newly-created enzyme works in a similar way. It knits together a 'copy' strand of RNA, using an original RNA strand as a reference or 'template,' according to the study published in the journal Nature.

But it doesn't clone a molecule that's identical to itself. Instead, it makes a mirror image of itself - like the left hand to its right. This means it can 'bond' more efficiently to develop a living form.  

No research team has ever made such so-called 'cross-chiral' enzymes before. 

The emergence of such enzymes in a primordial RNA world - which the new study shows was plausible - may have been key to creating the first forms of life.

'When I start to tell people about this, they sometimes wonder if we're merely suggesting the possibility of such an enzyme - but no, we actually made it,' said Professor Gerald Joyce, of the university.

As well as showing one possible path for life's beginnings, the breakthrough could provide a tool for evolving new molecules. An illustration of the western hemisphere in the Early Jurassic period (long after the first organisms evolved) is shown

Biology on Earth evolved in such a way that in each class of molecules, one 'chirality' or asymmetrical feature came to dominate. Virtually all RNA, for example, are 'right-handed' and called D-RNA.

The structural similarity of the enzyme to RNA makes interactions within that class more efficient - just as a handshake is more efficient when it joins two right or two left hands, rather than a left and a right.

'Scientists generally are taught to think that there has to be a common chirality among interacting molecules for biology to work,' Professor Joyce explained.

But his original study three decades ago showed that self-replicators would have had a tough time evolving in such a mix. 

'Since then we've all been wondering how RNA replication could have started on the primitive Earth,' he said.

The new enzyme was created using a technique called test-tube evolution.

Professor Joyce and post-doctoral researcher Jonathan Sczepanski started with a 'soup' of about a quadrillion short RNA molecules.

Their sequences were essentially random and all were 'right-handed.'

They deliberately set up the molecules to create a 'joining reaction' - so the right-handed molecules joined with the left. 

They could then be pulled out of the solution, and amplified.   

After 10 of these selection-and-amplification rounds, the researchers had a strong candidate ribozyme.

After technical tweaking, they had created the enzyme and intend on researching it further.

Professor Joyce said: 'Ultimately what one wants is to turn it loose, in the lab, of course, not in the wild, to let it start replicating and evolving and seeing what results.'