Mimicking natural evolution in a test tube, scientists have devised an enzyme with a unique property that might have been crucial to the origin of life on Earth.
Aside from illuminating one possible path for life’s beginnings, the achievement is likely to yield a powerful tool for evolving new and useful molecules.
The new enzyme is called a ribozyme because it is made from ribonucleic acid (RNA). Modern DNA-based life forms appear to have evolved from a simpler “RNA world,” and many scientists suspect that RNA molecules with enzymatic properties were Earth’s first self-replicators.
The new ribozyme works essentially in that way. It helps knit together a “copy” strand of RNA, using an original RNA strand as a reference or “template.” However, it doesn’t make a copy of a molecule completely identical to itself. Instead it makes a copy of a mirror image of itself — like the left hand to its right — and, in turn, that “left-hand” ribozyme can help make copies of the original.
No one has ever made such “cross-chiral” enzymes before. The emergence of such enzymes in a primordial RNA world — which the new study shows was plausible — could have overcome a key obstacle to the origin of life.
Biology on Earth evolved in such a way that in each class of molecules, one chirality, or handedness, came to predominate. Virtually all RNA, for example, are right-handed and called D-RNA. That structural sameness 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.