Resumen de Concepts, perspectives and implications of a hybrid system made of nucleic acids biopolymers and hydroxyapatite mineral
The origin of building blocks of life and how life thrived on Earth remains a topic of high interest for researchers of the Origin of Life. In this thesis, we deal with concepts, perspectives and implications of the system termed hydroxyolite, a combination of outstanding biopolymers (nucleic acids such as DNA and RNA) and an exceptional mineral (hydroxyapatite). First we study, based on Revilla et al. (2013) and Bertran et al. (2014), how hydroxyapatite forms crystals able to encapsulate DNA or RNA when nucleic acids are used as a nucleating template. Later, in Bertran et al., (2016), we reported the mechanism of how the encapsulated nucleic acid is released to the surroundings when environmental conditions change, for instance becoming more acidic. As a consequence, we postulated that DNA existing in cells can be encapsulated and protected by hydroxyapatite against environmental attacks (i.e. poisonous gases, gamma radiation or enzymatic degradation) until they change, making feasible the reintroduction of nucleic acids in the mainstream of life. We hypothesized about the implications of such a system in the early history of life when mass extinction events occurred on Earth (Turon et al., 2015). Moreover, we extended the hydroxyolite concept, borrowed from the materials chemistry, to other disciplines such as paleontology, biology, biotechnology and medicine by considering hydroxyolites as equivalents to non-viral vectors that can introduce and release DNA into a cell (transfection). Such nucleic acid triggers the expression of foreign proteins if released in the cytosol or might be recombined with cell genome when DNA is released in the target cell nucleus. In the second part of the thesis, we studied the hydroxyolite system from a complementary perspective. We speculate about the consequences of being hydroxyapatite the first actor and not the nucleic acid. We propose that hydroxyapatite might act as an inorganic mold if considered as a catalytic substrate that facilitates the synthesis of simple organic molecules as the building blocks of life. Thus, we identified a prebiotic scenario, a volcanic eruption under lightning, where a phenomenon known as dirty storm usually occurs under certain conditions. Hydroxyapatite is known in nature to be part of igneous rocks and volcanic ash in small but significant concentrations. We replicated in the laboratory such extreme conditions by developing a thermally and electrically stimulated polarization. A process performed at 1000 ºC and under a difference of potential of 300 kV·m-1, to obtain permanently polarized hydroxyapatite (Turon et al., 2016; PCT/EP2017/069437) that turned out to be an enhanced catalyst compared to hydroxyapatite able to fix nitrogen and carbon from a gas mixture of N2, CO2 and CH4 (Rivas et al., 2018). The catalyst, under UV light, converts them into amino acids (Glycine and D/L-Alanine) and small organic molecules by means of a new inorganic photosynthetic process. In this work, we develop an integrative prebiotic model that describes how simple molecules might be synthesized from mildly reducing atmospheres by combining previous models such as volcanos as giant reactors, minerals as catalysts and photochemical reactions in the atmosphere under prebiotic sun light. All of them under the framework of a prebiotic inorganic photosynthesis, a process that might be considered the corner stone of the rise of the building blocks of life.
