by Gert Korthof
Origin of life researcher and Nobel Prize winner Jack Szostak has made an important step towards creating a prebiotically plausible protocell (prebiotic implies that it did not originate from pre-existing forms of life, but its components could have self-assembled from raw materials available under physical and chemical conditions of the early earth). The protocell is a fatty acid vesicle, which is a simpler form of a cell membrane, in which RNA replication occurs autonomously without the help of enzymes. The results have been published in Science Nov 29 2013.
This is the first time that nonenzymatic RNA copying succeeded inside a fatty acid vesicle. The big obstacle has always been that magnesium ion Mg2+ was necessary for RNA copying, but two negative side-effects of high Mg2+ levels frustrated success. Firstly, high Mg2+ levels break down the simple, fatty acid membranes that probably surrounded the first living cells. Secondly, Mg2+ catalyses degradation of single-stranded RNA. After a long trial-and-error process, Szostak et al. discovered that citrate removes these two side-effects. Citrate efficiently protects fatty acid membranes from the disruptive effects of high Mg2+ ion concentrations, while both allowing RNA copying and protecting single-stranded RNA from Mg2+-catalyzed degradation.
An illustration of a protocell, composed of a fatty acid membrane encapsulating RNA ribozymes. © Exploring Life’s Origins.