Potential Origin of Primordial Protein Enzymes

Life on earth is facilitated by a multitude of enzymes that catalyze essential chemical reactions. The vast majority of today’s enzymes are proteins, yet looking at the complex and intricate structures of natural enzymes it is hard to imagine how the first enzymes emerged.

However, new experiments by Seelig and Szostak, show that small, simple enzymes can evolve rather easily. In the August 16, 2007 issue of Nature, they describe the generation of an artificial enzyme by simulating evolution in a test tube. The researchers at first produced a random library of 4 trillion small protein molecules that were all slightly different from each other and then isolated a new enzyme by subjecting those protein molecules to an in vitro process of selection and evolution. In a matter of a few weeks this procedure yielded the novel enzyme. This enzyme, an RNA ligase, catalyzes the joining of two RNA molecules – a reaction for which no natural enzymes are known.

This study presents a potential scenario for the origin of the earliest biopolymers that facilitated the chemical reactions supporting life. The successful creation of novel enzymes that are not derived from biological proteins sheds new light on the potential of life beyond earth.

Aug 21, 2008

Robert Shapiro said:

Seelig and Szostak have used cutting-edge biotechnology techniques to demonstrate a novel path for the discovery of new enzymatic activities. As described by Michael P. Robertson and William G. Scott in a commentary published in the same issue of Nature on August 16, 2007: “They use an in vitro artificial selection process to isolate new protein enzymes that join the ends of two RNA molecules together.” Their procedure is highly innovative and offers promise for the development of new proteins of medical and commercial importance. However, it offers no insight into the question of how life first began on the early Earth. The authors started with a library of protein sequences. The starting library was was undoubtedly prepared with the aid of a commercial synthesizer that employed pure, chiral monomers. A number of technologically -advanced selection strategies were applied by the investigators to attain a result desired by them. It is extremely unlikely that pure homopolymers were present on the prebiotic Earth, and there were certainly no scientists and laboratories available at that time. In our admiration for the achievements of contemporary humans, we must not fall into the trap of assuming that blind, uninformed nature could have carried out the same steps.