Abstract
The RNA World hypothesis presupposes that abiotic reactions originally produced nucleotides, the monomers of RNA and universal constituents of metabolism. However, compatible prebiotic reactions for the synthesis of complementary (that is, base pairing) nucleotides and mechanisms for their mutual selection within a complex chemical environment have not been reported. Here we show that two plausible prebiotic heterocycles, melamine and barbituric acid, form glycosidic linkages with ribose and ribose-5-phosphate in water to produce nucleosides and nucleotides in good yields. Even without purification, these nucleotides base pair in aqueous solution to create linear supramolecular assemblies containing thousands of ordered nucleotides. Nucleotide anomerization and supramolecular assemblies favour the biologically relevant β-anomer form of these ribonucleotides, revealing abiotic mechanisms by which nucleotide structure and configuration could have been originally favoured. These findings indicate that nucleotide formation and selection may have been robust processes on the prebiotic Earth, if other nucleobases preceded those of extant life.
Highlights
The RNA World hypothesis presupposes that abiotic reactions originally produced nucleotides, the monomers of RNA and universal constituents of metabolism
These heterocycles are well suited to function as the recognition units of a primitive informational system, as barbituric acid (BA) and melamine: (i) are produced in the same model prebiotic reaction[25]; (ii) can form Watson–Crick-like base pairs with each other[26]; (iii) have H-bond donor and acceptor groups that are complementary with uracil and adenine, making these heterocycles ‘forward compatible’ for base pairing with two extant nucleobases[9]; (iv) possess chemical properties that indicate favourable glycosylation by ribose, at the C5 position of BA and the exocyclic amines of melamine
Given previous reports that phosphorylated sugars can be produced in model prebiotic reactions[7], we were motivated to explore the potential for BA and melamine to be glycosylated by R5P, which could represent a model prebiotic route to nucleotides that can form base pairs that are similar to those formed by the canonical nucleobases (Fig. 1a)
Summary
The RNA World hypothesis presupposes that abiotic reactions originally produced nucleotides, the monomers of RNA and universal constituents of metabolism. We report the glycosylation reactions and nucleotide assembly/mutual selection of two candidate protonucleobases, barbituric acid (BA) and melamine These heterocycles are well suited to function as the recognition units of a primitive informational system, as BA and melamine: (i) are produced in the same model prebiotic reaction[25]; (ii) can form Watson–Crick-like base pairs with each other[26]; (iii) have H-bond donor and acceptor groups that are complementary with uracil (for melamine) and adenine (for BA), making these heterocycles ‘forward compatible’ for base pairing with two extant nucleobases[9]; (iv) possess chemical properties that indicate favourable glycosylation by ribose, at the C5 position of BA and the exocyclic amines of melamine. These findings demonstrate prebiotically plausible mechanisms for the selection of nucleotides in both nucleobase and sugar structure
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