Lecture 25 B (real)

Lecture 25 B (real) - Lecture 25 Protein Folding,...

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Lecture 25 Protein Folding, Modification and Degradation Form follows function Function is form Polypeptide synthesized with a particular amino acid structure: Must fold into the proper 3D conformation with the appropriate secondary, tertiary and possibly quaternary structure Native state : Proteins can adopt only one or just a few very closely related characteristic functional conformations Most stable form of the molecule Properties that limit folding: Properties of side chains Sequence along the peptide backbone Denaturants : Perturbations that alter the charges on amino acid side chains Denaturation : Disruption of the weak noncovalent interactions that stabilize the native conformation of a protein Protein Folding Issue for polypeptide : Wants the hydrophobic residues to be buried away from water while exposing the hydrophilic residues to water as much as it can Start with unfolded polypeptide in order to arrive at a folded conformation in acqueous environment: Not simple because if you start the wrong way it might end up stuck Page | 1
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Protein is usually divided in "folding units" which are domains: Restrict it to a length that has a chance of folding properly Longer lengths are not efficient and folding may fail Protein folding: in vitro conversation between native and denatured conformations All the information for the final perfectly balanced structure of the domain is contained in the sequence A peptide can do it on its own successfully Problem : it might fail to do it - not 100% efficient Experiment 1.Take a native protein (red conformation) 2.Put it in a urea solution Binds water very strongly and "steals" it from the protein Protein loses its water and starts to denature Completely unfolded protein 1.Try to renature the protein by decreasing the urea concentration Exchange a buffer with another one Method : Dialysis You can succeed in obtained the exact same protein through this experiment: Always have a % that will "fail" What is fail? Fails to achieve folded conformation in aqueous environment
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Lecture 25 B (real) - Lecture 25 Protein Folding,...

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