A ribosome in action
The manufacture of proteins by ribosomes involves complex interactions of diverse nucleic-acid and protein ligands. Single-molecule studies allow for the first time, scientists to follow the synthesis of full-length proteins in real time.
This is clearly demonstrated in articles by Bakmann and Uemera et al in Nature 15th April 2010 .
Protein synthesis involves a complex interplay of various cellular components. Ribosomes are the cell’s protein-production factories, and interact with messenger RNA (the template), amino-acylated transfer RNAs (which act as adaptors between mRNA and amino-acid residues) and diverse co-factors (for the initiation of synthesis, elongation of the nascent chain and release of the mature polypeptide). Uemura et al. report the use of an extremely sensitive single-molecule detection technique to observe this process at unprecedented resolution: the stepwise synthesis of a single protein.
Ribosomes are evolutionarily conserved molecular nanomachines with a diameter of about 25 nanometres and a molecular weight of around 2.5 megadaltons. In functional terms, they are amino-acid polymerase enzymes with an RNA ‘heart’. They accelerate the rate of protein synthesis by at least one millionfold, owing exclusively to entropic effects that involve the positioning of aminoacyl- tRNAs, the shielding of the reaction from bulk solvent and the organ-ization of their own active site. Ribosomes also check the quality of their polypeptide products – as inaccurate amino-acid sequences could result in an altered three-dimensional protein structure and even cellular toxicity.
Structural analyses of functional ribosome complexes have formed the basis of a consistent biochemical model for the mechanism of protein synthesis, suggesting that this process depends on large-scale conformational changes in the ribosome. But the nature, timescale and magnitude of these dynamic changes have until now remained undefined.
Brakmann 2010 A ribosome in action Nature vol 464 987-8
Uemura et al 2010 Real time t RNA transit on single translating ribosomes at codon resolution Nature vol 464, 1012-1017
- Martin Eastwood