The Dimeric Proto-Ribosome Within the Modern Ribosome
A structural element that could have existed independently in the prebiotic era was identified at the active site of the contemporary ribosome’s large subunit. It is suggested to have functioned as a proto-ribosome, catalyzing noncoded peptide bond formation and primitive elongation. This simple apparatus, constructed from a dimer of small, self-folding, stable RNA molecules, structurally related to tRNA, could have assembled spontaneously under prebiotic conditions. Its structure enabled the catalysis of peptide bond formation in the same manner that the contemporary ribosome exerts positional catalysis by accommodating the two reactants in a stereochemistry favorable for peptide bond formation. This prebiotic entity, which was efficient and stable enough to be retained by evolution as the highly conserved active site of the ribosome, was the matrix from which the modern protein biosynthesis mechanism – common to all living organisms – has evolved.
KeywordsDomain Versus Peptide Bond Formation Symmetrical Region Peptidyl Transferase Center Core Molecule
Thanks are due to Ada Yonath for initiating the ribosome evolution study and to Amitai Halevi, Noam Adir, Sagi, and Nimrod Agmon for their help. Support was provided by the US National Inst. of Health (GM34360) and the Kimmelman Center for Macromolecular Assemblies.
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