How early life did without enzymes

AMYLOID plaques are a sign of Alzheimer’s disease, and bad news for humans. But these clusters  of proteins could have driven the earliest life on Earth. They can behave as catalysts, a finding  that lends weight to a theory  that amyloids helped to trigger  life-sustaining reactions before enzymes evolved. Without enzymes, metabolic reactions would not occur. But enzymes are big proteins folded into specific shapes, so it is hard to see how they could have appeared fully formed in the primordial soup where life may have evolved There is a mind-bogglingly vast number of possible enzymes – 20100 – each with a different structure. Very few of these will be useful because enzymes have to be an exact fit for the chemical they react with, just as a lock can only be opened by a specific key. Even given millions of years, nature would have struggled to produce the enzymes that catalyse today’s metabolic reactions, claims Ivan Korendovych at Syracuse University in New York. Amyloids could be the solution. Unlike enzymes, they contain peptides – short chains of amino acids – and could have evolved more easily. If a bunch of short peptides are mixed together, amyloids form, each with a complex structure.  To see if these amyloids behave like enzymes, Korendovych and his colleagues made seven simple peptides, each seven amino acids long. They then made amyloids  by allowing copies of each peptide to clump together, adding zinc ions to help the process along. Four of the seven peptides made amyloids that could break down organic molecules called esters (Nature Chemistry, doi.org/ rxf). “No one has shown before that peptides this short can selfassemble to become enzyme-like catalysts,” says Korendovych. The result suggests that such STEP INSIDE THE WORLD’S GREATEST EXPERIMENT AT THE SCIENCE MUSEUM FINAL WEEKS Until 5 May 2014 Book now sciencemuseum.org.uk/collider  South Kensington   @sciencemuseum #smCollider MAJOR SPONSORS MEDIA PARTNER simple amyloids could have been nature’s prototype enzymes. Later, the amyloids could have acted as a stepping stone for the evolution of today’s large enzymes. “It’s an outstanding paper,” says Ehud Gazit at Tel Aviv University in Israel. Gazit helped develop the theory that short peptides were the first enzymes, but was not involved in the new research. “This study brings it  to a new level by demonstrating catalytic properties comparable to enzymes,” he says. The amyloid theory has legs, but the new study could have provided a better demonstration, says James Milner-White at the University of Glasgow, UK. “They have not chosen the right metal ion,” he says. Zinc was rare in the early oceans, while iron and nickel were more common, so MilnerWhite wants to know if they could also help the amyloids form.  ■