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Crystal structure of the eukaryotic ribosome. – F1000

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from sciencephoto

This work describes for the first time the overall structure of the eukaryotic ribosome from yeast at 4.15 angstrom resolution, which reveals a considerably larger assembly and thus a greater degree of complexity than its prokaryotic counterpart. Despite significant differences between the structure of eukaryotic and prokaryotic ribosomes, the basic architecture remains similar.

Although structures have been reported for the large ribosomal subunit (50S) from Haloarcula marismortui {1} and the small ribosomal subunit (30S) from Thermus thermophilus {2}, the structure for the eukaryotic ribosome was unknown and, despite the conservation of both sequence and function among ribosomes, the eukaryotic ribosome was expected to contain significant differences in structure given the 40% increase in its size compared to its bacterial counterpart. The larger size of the eukaryotic ribosome results from the inclusion of rRNA expansion elements and ribosomal proteins unique to eukaryotes. The authors show that the rRNA expansion elements are located predominantly on the solvent-exposed sides at the periphery of both subunits and they suggest functions for several of these expansion elements and ribosomal proteins in translation initiation and elongation. Considerable differences in structure were observed for the entry and exit sites of the mRNA on the small subunit, suggesting roles that may be unique to eukaryotes, e.g. interactions with mRNA and initiation factors. In contrast to many of the observed differences, the intersubunit bridges observed in the crystal structure of the bacterial ribosome have corresponding bridges in the eukaryotic ribosome. Although this new structure of the complete 80S eukaryotic ribosome provides a basis for understanding the differences in structure between eukaryotic ribosomes and those in other kingdoms, it raises new questions about the roles of the rRNA expansion elements and the eukaryotic-specific ribosomal proteins that only additional high-resolution structures of the eukaryotic ribosomes in conjunction with tRNA, mRNA, initiation, elongation, and termination factors will be able to answer.

References:
{1} Ban et al. Science 2000, 289:905-20 [PMID:10937989].
{2} Jenner et al. Nat Struct Mol Biol 2010, 17:1072-8 [PMID:20694005].

Competing interests: None declared

Gallie D: “This work describes for the first time the overall structure of the eukaryotic ribosome from…” Evaluation of: [Ben-Shem A et al. Crystal structure of the eukaryotic ribosome. Science. 2010 Nov 26;
330(6008):12039; doi: 10.1126/science.1194294]. Faculty of 1000, 15 Feb 2011. F1000.com/6750956

Short form
Gallie D: 2011. F1000.com/6750956

 

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The large subunit of the ribosome. Starburst, active site for protein synthesis. The active site consists of RNA (white strands), not protein (orange), supporting the conclusion that the ribosome is a ribozyme.
Figure by Nenad Ban and Thomas Steitz
Copyright © Howard Hughes Medical Institute

 

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