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Clément Blanchet

Protein refolding and amyloid fiber formation: A case study with α-lactalbumin

Published on 23 June 2008


Thesis presented June 23, 2008

Abstract:
Protein folding is one of the central questions of Biology. How does polypeptidic chain fold to its three-dimensional, biologically active, structure? Experiments done in the 60’s have shown that the folded form is the most stable one on a thermodynamic point of view. This form being defined by the primary structure of the protein, the folding reaction corresponds to the last step of the use of the information encoded in DNA. Proteins can sometimes misfold and form amyloid fibrils through intermolecular interactions. These structured aggregates are involved in several diseases such as Alzheimer’s disease, Parkinson diseases…
These phenomenon's are studied here in the case of
α-lactalbumin, a milk protein which possesses a calcium binding site. At first, the folding is monitored in presence of various metal ions that bind to the calcium site. These experiments are coupled with thermal unfolding experiments. They permit to precise the effect of metal ion binding on the different states of the protein and on the folding kinetics.
The reaction is also monitored in the absence​ of metal ions with several biophysical methods. Then, the folding is much slower and intricate. A reaction scheme is drawn from the results. This scheme indicates that a state precursor of amyloid fibril is transiently populated during the reaction. Finally, the effect of intermolecular interactions on the formation of amyloid fibrils is characterized for different salt concentrations.

Keywords:
Protein folding, amyloid fibrils,
α-lactalbumin, metallic cofactor, spectroscopy, energy landscape

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