Abstract EANA2024-89

Thermal proteinoids are polyamino acids that are thermally condensed polyamino acids derived from amino acids and/or their precursors. These molecular weights are approximately several thousands, as determined by gel permeation chromatography, and have relatively longer results. This indicates that thermal proteinoid is a relatively longer polyamino acid formed under prebiotic conditions. Furthermore, Harada et al. reported that thermal proteinoids form micron-size spherical structures by dissolving and cooling in hot water. It is hypothesized that the spherical structures, called as proteinoid microspheres, may be regarded as self-assembled structures of thermal proteinoids and represent the initial stage of the protocells. It is postulated that the addition of a function is necessary for the microsphere to undergo the transition to a protocell. Consequently, in this study, we investigated the adsorption and uptake of various organic molecules as a preliminary step towards the functionalization of the microsphere.

In the report by Harada et al., the diameter of proteinoid microspheres was found to be regulated by the concentration of potassium ions, suggesting that self-assembly occurs due to electrostatic interactions. Conversely, the molecular structure of thermal proteinoids synthesized from monoammonium malate was analyzed, revealing that the main component was a polyimide ring with less hydrophilicity than the highly hydrophilic free carboxyl group. Consequently, a variety of fluorescent dyes were added to the protienoid microspheres suspension and observed under a fluorescence microscope. The microspheres were stained with Lipi-Green and PlasMem Bright Green, which are known to stain lipid droplets and cell membranes, respectively. These results indicate that the microspheres have a hydrophobic environment and that the mechanism of self-assembly would be hydrophobic interactions.

In the context of protocells, it is essential that nucleic acids and polyamino acids interact with one another. Consequently, an investigation was conducted to ascertain whether nucleic acids could be incorporated into proteinoid microspheres. Salmon sperm DNA fragments and lambda DNA solution were dropped into the microspheres suspension. Subsequently, the microspheres suspension was dried and observed using an electron probe microanalyzer (EPMA). The accumulation of carbon and nitrogen derived from proteinoid in the microspheres was confirmed, and at the same time, a signal for phosphorus derived from nucleic acids was observed. This indicated that nucleic acids had interacted with the microspheres. Even after the nucleic acids had been interacted with the microspheres, the microspheres were subjected to heating to melt them and then reconstitution. A phosphorous signal was also observed at the same location on the microspheres. This indicates a strong interaction between proteinoids and nucleic acids.

At this time, it is unclear whether the organic compounds are adsorbed to the surface of the microspheres or incorporated into the microspheres. We are currently engaged in research to elucidate this matter.