Origin & Evolution of Life

Did The Exposure Of Coacervate Droplets To Rain Make Them The First Stable Protocells?

By Keith Cowing

Status Report

Science via PubMed

October 30, 2024

Filed under Membraneless coacervate microdroplet, microdroplets, origin of life, prebiotic, protocell, Rain, RNA

Did The Exposure Of Coacervate Droplets To Rain Make Them The First Stable Protocells? — Droplet bioreactors demonstrating chemical communication. (A) Schematic of enzyme cascade in droplets and the corresponding droplet-to-droplet chemical communication. (B) Confocal micrographs showing the time evolution of resorufin fluorescence (red channel) in PDDA-ATP coacervate droplets with CF488-GOx (green channel) and CF640-HRP (blue channel) enzymes as cargo. Glucose and amplex red were introduced into the solution surrounding the droplets, and the resultant resorufin fluorescence first appeared in HRP droplets (merged channel color change from blue to purple to pink) and then in GOx (color change from green to yellow) droplets. Scale bars, 30 μm. A set of images from another independent trial of the same experiment are shown in fig. S7, where similar features were found. (C) A plot of time evolution of resorufin fluorescence intensity in stabilized droplets during enzyme catalysis. For each time point, normalized intensity corresponds to area fraction of HRP (or Gox) protocell covered by resorufin fluorescence, n = 4 images were analyzed, and error bars represent SDs. Science via PubMed

Membraneless coacervate microdroplets have long been proposed as model protocells as they can grow, divide, and concentrate RNA by natural partitioning.

However, the rapid exchange of RNA between these compartments, along with their rapid fusion, both within minutes, means that individual droplets would be unable to maintain their separate genetic identities. Hence, Darwinian evolution would not be possible, and the population would be vulnerable to collapse due to the rapid spread of parasitic RNAs.

In this study, we show that distilled water, mimicking rain/freshwater, leads to the formation of electrostatic crosslinks on the interface of coacervate droplets that not only suppress droplet fusion indefinitely but also allow the spatiotemporal compartmentalization of RNA on a timescale of days depending on the length and structure of RNA. We suggest that these nonfusing membraneless droplets could potentially act as protocells with the capacity to evolve compartmentalized ribozymes in prebiotic environments.

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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