The structure fo the 40S ribosomal subunit of eukaryotic ribosomes has recently been determined through x-ray crystallography, a method that allows scientists to reconstruct a 3-dimensional model of a protein in its native conformation. This discovery represents a significant breakthrough that scientists are hopeful will lead to an understanding of the evolution of ribosomes and eukaryote-specific mechanisms of protein synthesis.
Ribosomes, the small organelles that exist in millions of copies in all living cells, are responsible for one of life’s most essential processes- the creation of specific proteins with millions of different functions. Composed of a small and a large “subunit”, ribosomes are essentially tiny factories that process RNA and match specific RNA sequences with the amino acids necessary for building a particular protein. Because of this vital role, they have remained relatively highly conserved over evolutionary time. However, enough changes have accrued in ribosomes that, over time, they have become important biomarkers for distinguishing species. This technique has proved incredibly useful in describing the diversity of microbial communities. In particular, when scientists want to get a sense of the ” species diversity” in a particular environmental sample, extraction and genetic sequencing of the small ribosomal subunit has become the gold standard.
Compared to prokaryotes, less is known about the structure and function of the eukaryotic ribosome. Not only are eukaryotic ribsomes larger and somewhat more complex, eukaryotic protein synthesis involves complex regulation and feedback pathways that are not present in prokaryotes. For example, the new crystal structure of the 40S subunit, or small eukaryotic ribosome subunit, reveals an interaction with a small protein known as an “initiation factor” that helps signal the ribsome to begin produciton of a new protein. The small subunit is responsible for binding numerous such initiation factors, and the new 3D structure promises to provide insight into eukaryotic-specific aspects of proteins synthesis, as well insight into the evolution of ribsomes by comparison of structures across a diverse range of species.