Thursday, June 6, 2013

The origin of the ribosome is in mechanics, not protein synthesis

The origin and evolution of modern biochemistry is a complex problem that has puzzled scientists for almost a century. While comparative, functional and structural genomics has unraveled considerable complexity at the molecular level, there is very little understanding of the origin, evolution and structure of the molecules responsible for cellular or viral features in life. The ribosome is the most central macromolecular complex of the cell. It is responsible for protein synthesis and its biosynthetic functions set cells apart from viruses. the origin of this ensemble is mysterious. Proponents of the ancient 'RNA world' postulate that the ribosome was originally an RNA enzyme (a ribozyme) that was responsible for genetics. A recent paper by Harish and Caetano-Anollés (PLoS ONE 7 (3): e32776, 2012) challenge this scenario and the possible existence of an RNA world.Deep historical signal was retrieved from a census of molecular structures and functions in thousands of nucleic acid and protein structures and hundreds of genomes using powerful phylogenomic methods. Together with structural, chemical and cell biology considerations, this information reveals that the ribosome is the result of gradual and coordinated evolutionary appearance of molecular parts of RNA and ribosomal proteins. These coevolutionary patterns comply with the principle of continuity and falsify the existence of an ancient RNA world. Instead they are compatible with a model of gradually co-evolving nucleic acids and proteins in interaction with increasingly complex cofactors, lipid membrane structures and other cellular components (Caetano-Anollés et al., J. Mol. Evol. 74 (1-2): 1-34, 2012). This changes the perception we have of the rise of modern biochemistry and prompts further analysis of the emergence of biological complexity in an ever-expanding coevolving world of macromolecules (Caetano-Anollés and Seufferheld, J. Mol. Microbiol. Biotechnol. 23 (1-2): 152-177, 2013).

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