A New Clue to the Origin of Life

To get biology you need enzymes, but where did enzymes come from?

Single-celled organisms may look simple, but they require some pretty advanced chemistry.

The smallest unit of life, the cell, can’t function without enzymes. These proteins, typically made of at least 100 amino acids folded into a three-dimensional structure, catalyze thousands of biochemical reactions. They allow organisms to increase dramatically the rate of chemical reactions, sometimes by a factor of a million, over what would occur in the absence of biology.

Enzymes must have been critical for the origin of life. But there’s a problem: Today’s enzymes are so large and complex that it’s difficult to see how they could have evolved in Darwin’s little pond, or in any other primordial environment that’s been proposed. It would have been extremely unlikely for a protein made of 100 amino acids to assemble by chance, in just the right order to catalyse a particular reaction.

Clearly, the first enzymes (let’s call them instead bio-catalyzers, or chemical compounds that enhanced a biologically important reaction without changing themselves) must have been much simpler.  This is exactly what Ivan Korendovych and Caroline Rufo of Syracuse University and their colleagues report in a new paper published in Nature Chemistry. They show that much shorter, “amyloid forming” peptides could in fact have served as bio-catalysers—from which enzymes may have evolved later.

Interestingly, amyloids are familiar to medical researchers, who suspect that these “misfolded” polypeptides and proteins play a role in Alzheimer’s disease. It wouldn’t be the first time that a biochemical “invention” from the early days of life on Earth would haunt us today as an agent of disease.

Korendovych and colleagues found that short (just seven amino acid-long) amyloid peptides with zinc as a metal ion have catalytic properties. The research would have been even more convincing if it were iron instead of zinc, since iron is thought to have been much more available on the early Earth. But it’s an interesting result nonetheless.

Along with peptides and proteins, primitive life would have needed membranes to contain the contents of a cell, and some kind of template molecule—simpler than today’s DNA—for passing information from one generation to the next. All three developments would have had to arise at roughly the same time and place; two out of three wouldn’t result in a functioning cell. So we still have a long way to go in solving the puzzle of life’s origin.

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