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Co-translational protein folding


Schematic view of a 50S subunit of a ribosome tethered to the surface of a cover slide

It is well known that protein folding in the cell is very different from a typical in vitro refolding scenario which is generally used for protein folding studies. The major difference is related to the fact that in the cell the nascent polypeptide chain as synthesized by the ribosome starts already to fold during synthesis and chain elongation.
An important question is how cotranslational folding ensures more effective and productive folding than refolding from full-length polypeptides. First, during synthesis and protein folding, the elongating nascent chain remains bound to the ribosome and has less rotational and translational freedom. This restriction can significantly reduce intermolecular collisions with other (in particular, also not yet folded) proteins and thereby suppress aggregation. Second, in contrast to refolding, folding of N-terminal and C-terminal regions is separated spatially and temporally during sequential synthesis. Most probably, this prevents unwanted interactions that often lead to off-pathway folding intermediates or aggregates. Third, several chaperones (e.g., the trigger factor in bacteria) act already during translation on the nascent chain and prevent misfolding or aggregation.
To study co-translational protein folding, we use time resolved single molecule fluorescence microscopy. We tether single ribosomes on a surface and we follow the time-course of single in-situ synthesized green fluorescence proteins (GFP) using a confocal or a wide-field fluorescence microscope. The ambitious objective of this project is to follow folding events of individual polypeptides and proteins while they are associated with ribosomes during translation by employing FRET (co-translational folding). (Katranidis et al., Angew. Chem. Int. Edit. 2009, 48, 1758-1761)



Fluorescence of emerging GFP molecules bound on single ribosomes which are tethered on a surface

Contact: Dr. Alexandros Katranidis