Modern organisms commonly use the same set of 20 genetically coded amino acids for protein synthesis with very few exceptions. However, earlier protein synthesis was plausibly much simpler than modern one and utilized only a limited set of amino acids. Nevertheless, few experimental tests of this issue with arbitrarily chosen amino acid sets had been reported prior to this report. Herein we comprehensively and systematically reduced the size of the amino acid set constituting an ancestral nucleoside kinase that was reconstructed in our previous study. We eventually found that two convergent sequences, each comprised of a 13-amino acid alphabet, folded into soluble, stable and catalytically active structures, even though their stabilities and activities were not as high as those of the parent protein. Notably, many but not all of the reduced-set amino acids coincide with those plausibly abundant in primitive Earth. The inconsistent amino acids appeared to be important for catalytic activity but not for stability. Therefore, our findings suggest that the prebiotically abundant amino acids were used for creating stable protein structures and other amino acids with functional side chains were recruited to achieve efficient catalysis.
Quasi-one-dimensional (quasi-1D) fibrous red phosphorus (RP) has triggered growing interest recently for its unique properties and promising applications in energy storage, sensing, and heterogeneous catalysis. However, attempts to explore its anisotropy and transport properties have progressed slowly. In this work, we report the fabrication of large-size and pure bulk fibrous RP crystals using a chemical vapor transport reaction by modifying growth kinetics. For the first time, the weak layer number-dependent anisotropic electronic structure of fibrous RP is revealed based on theoretical calculations. The b-axis-aligned fibrous RP nanoribbons with a high aspect ratio exceeding 1000 are easily prepared by facile liquid exfoliation. Impressively, the field-effect transistor device built with fibrous RP nanoribbons exhibits p-type transport behavior and a high mobility reaching 236.7 cm 2 V −1 s −1 with an On/Off ratio approaching 1.6 × 10 3 , which are superior to those of other reported RP-based materials in general. The results demonstrate the great potential of fibrous RP as a promising channel material and lay a solid foundation to further study the intrinsic properties of quasi-1D van der Waals materials.
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