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The RNA world and the origin of metabolic enzymes.

Ralser M - Biochem. Soc. Trans. (2014)

Bottom Line: Recently, we described a non-enzymatic glycolysis and pentose phosphate pathway-like reactions catalysed by metal ions [mainly Fe(II)] and phosphate, simple inorganic molecules abundantly found in Archaean sediments.Interestingly, considering a metal-catalysed origin of metabolism gives rise to an attractive hypothesis about how the first enzymes could have formed: simple RNA or (poly)peptide molecules could have bound the metal ions, and thus increased their solubility, concentration and accessibility.In a second step, this would have allowed substrate specificity to evolve.

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ABSTRACT
An RNA world has been placed centre stage for explaining the origin of life. Indeed, RNA is the most plausible molecule able to form both a (self)-replicator and to inherit information, necessities for initiating genetics. However, in parallel with self-replication, the proto-organism had to obtain the ability to catalyse supply of its chemical constituents, including the ribonucleotide metabolites required to replicate RNA. Although the possibility of an RNA-catalysed metabolic network has been considered, it is to be questioned whether RNA molecules, at least on their own, possess the required catalytic capacities. An alternative scenario for the origin of metabolism involves chemical reactions that are based on environmental catalysts. Recently, we described a non-enzymatic glycolysis and pentose phosphate pathway-like reactions catalysed by metal ions [mainly Fe(II)] and phosphate, simple inorganic molecules abundantly found in Archaean sediments. While the RNA world can serve to explain the origin of genetics, the origin of the metabolic network might thus date back to constraints of environmental chemistry. Interestingly, considering a metal-catalysed origin of metabolism gives rise to an attractive hypothesis about how the first enzymes could have formed: simple RNA or (poly)peptide molecules could have bound the metal ions, and thus increased their solubility, concentration and accessibility. In a second step, this would have allowed substrate specificity to evolve.

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Did metal-based catalysis facilitate the formation of the first metabolic enzymes?(a) A precursor of glycolysis and the PPP was catalysed by ferrous iron and other metals found in the prebiotic oceans. (b) RNA molecules (and/or peptides?) bound the metal ions and in that way increased their accessibility and potentially their local concentration. (c) Positive selection of more sophisticated structures achieved specificity by preventing contact of the metal catalyst with some of the metabolites, and increasing the affinity for others.
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Figure 1: Did metal-based catalysis facilitate the formation of the first metabolic enzymes?(a) A precursor of glycolysis and the PPP was catalysed by ferrous iron and other metals found in the prebiotic oceans. (b) RNA molecules (and/or peptides?) bound the metal ions and in that way increased their accessibility and potentially their local concentration. (c) Positive selection of more sophisticated structures achieved specificity by preventing contact of the metal catalyst with some of the metabolites, and increasing the affinity for others.

Mentions: Finally, RNA or peptide binding could increase the specificity of a reaction: metal ions such as Fe(II) act on a broad set of substrates. They are thus in many cases also catalysing unwanted reactions [40]. An example in modern cells is the Fenton reaction where ferrous iron produces superoxide from hydrogen peroxide, causing anything from oxidative stress up to fatal cellular toxicity [41]. To avoid Fenton chemistry, modern cells evolved a complex iron transport system and to circumvent the presence of ferrous iron in their cytoplasm [42]. Reflected in the primordial world, RNA structures could have prevented certain substrates from reaching the metal catalyst, and increased the affinity for others. A first enzyme would have been born (Figure 1).


The RNA world and the origin of metabolic enzymes.

Ralser M - Biochem. Soc. Trans. (2014)

Did metal-based catalysis facilitate the formation of the first metabolic enzymes?(a) A precursor of glycolysis and the PPP was catalysed by ferrous iron and other metals found in the prebiotic oceans. (b) RNA molecules (and/or peptides?) bound the metal ions and in that way increased their accessibility and potentially their local concentration. (c) Positive selection of more sophisticated structures achieved specificity by preventing contact of the metal catalyst with some of the metabolites, and increasing the affinity for others.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4128644&req=5

Figure 1: Did metal-based catalysis facilitate the formation of the first metabolic enzymes?(a) A precursor of glycolysis and the PPP was catalysed by ferrous iron and other metals found in the prebiotic oceans. (b) RNA molecules (and/or peptides?) bound the metal ions and in that way increased their accessibility and potentially their local concentration. (c) Positive selection of more sophisticated structures achieved specificity by preventing contact of the metal catalyst with some of the metabolites, and increasing the affinity for others.
Mentions: Finally, RNA or peptide binding could increase the specificity of a reaction: metal ions such as Fe(II) act on a broad set of substrates. They are thus in many cases also catalysing unwanted reactions [40]. An example in modern cells is the Fenton reaction where ferrous iron produces superoxide from hydrogen peroxide, causing anything from oxidative stress up to fatal cellular toxicity [41]. To avoid Fenton chemistry, modern cells evolved a complex iron transport system and to circumvent the presence of ferrous iron in their cytoplasm [42]. Reflected in the primordial world, RNA structures could have prevented certain substrates from reaching the metal catalyst, and increased the affinity for others. A first enzyme would have been born (Figure 1).

Bottom Line: Recently, we described a non-enzymatic glycolysis and pentose phosphate pathway-like reactions catalysed by metal ions [mainly Fe(II)] and phosphate, simple inorganic molecules abundantly found in Archaean sediments.Interestingly, considering a metal-catalysed origin of metabolism gives rise to an attractive hypothesis about how the first enzymes could have formed: simple RNA or (poly)peptide molecules could have bound the metal ions, and thus increased their solubility, concentration and accessibility.In a second step, this would have allowed substrate specificity to evolve.

View Article: PubMed Central - PubMed

ABSTRACT
An RNA world has been placed centre stage for explaining the origin of life. Indeed, RNA is the most plausible molecule able to form both a (self)-replicator and to inherit information, necessities for initiating genetics. However, in parallel with self-replication, the proto-organism had to obtain the ability to catalyse supply of its chemical constituents, including the ribonucleotide metabolites required to replicate RNA. Although the possibility of an RNA-catalysed metabolic network has been considered, it is to be questioned whether RNA molecules, at least on their own, possess the required catalytic capacities. An alternative scenario for the origin of metabolism involves chemical reactions that are based on environmental catalysts. Recently, we described a non-enzymatic glycolysis and pentose phosphate pathway-like reactions catalysed by metal ions [mainly Fe(II)] and phosphate, simple inorganic molecules abundantly found in Archaean sediments. While the RNA world can serve to explain the origin of genetics, the origin of the metabolic network might thus date back to constraints of environmental chemistry. Interestingly, considering a metal-catalysed origin of metabolism gives rise to an attractive hypothesis about how the first enzymes could have formed: simple RNA or (poly)peptide molecules could have bound the metal ions, and thus increased their solubility, concentration and accessibility. In a second step, this would have allowed substrate specificity to evolve.

Show MeSH
Related in: MedlinePlus