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Life 2017, 7(3), 33; doi:10.3390/life7030033

Characterization of Reconstructed Ancestral Proteins Suggests a Change in Temperature of the Ancient Biosphere

Faculty of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan
Received: 19 July 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 6 August 2017
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Abstract

Understanding the evolution of ancestral life, and especially the ability of some organisms to flourish in the variable environments experienced in Earth’s early biosphere, requires knowledge of the characteristics and the environment of these ancestral organisms. Information about early life and environmental conditions has been obtained from fossil records and geological surveys. Recent advances in phylogenetic analysis, and an increasing number of protein sequences available in public databases, have made it possible to infer ancestral protein sequences possessed by ancient organisms. However, the in silico studies that assess the ancestral base content of ribosomal RNAs, the frequency of each amino acid in ancestral proteins, and estimate the environmental temperatures of ancient organisms, show conflicting results. The characterization of ancestral proteins reconstructed in vitro suggests that ancient organisms had very thermally stable proteins, and therefore were thermophilic or hyperthermophilic. Experimental data supports the idea that only thermophilic ancestors survived the catastrophic increase in temperature of the biosphere that was likely associated with meteorite impacts during the early history of Earth. In addition, by expanding the timescale and including more ancestral proteins for reconstruction, it appears as though the Earth’s surface temperature gradually decreased over time, from Archean to present. View Full-Text
Keywords: ancestral sequence reconstruction; ancient biosphere; last universal common ancestor; phylogenetic analysis; Precambrian; thermophilicity ancestral sequence reconstruction; ancient biosphere; last universal common ancestor; phylogenetic analysis; Precambrian; thermophilicity
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Akanuma, S. Characterization of Reconstructed Ancestral Proteins Suggests a Change in Temperature of the Ancient Biosphere. Life 2017, 7, 33.

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