MBB222-lecture8

MBB222-lecture8 - most proteins can fold without...

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• most proteins can fold without assistance, in a co-translational anner manner • yet, some proteins have difficulty folding properly, and need the assistance of chaperones – a class of proteins found in all organisms • 2 types molecular chaperones : bind and stabilize unfolded or partially folded proteins (usually hydrophobic residues), thus preventing aggregation or degradation pg g g g g » e.g., eukaryotic Hsp70 prokaryotic DnaK – bind nascent polypeptides as they are being synthesized by the ribosomes
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85% of proteins, once released from their molecular chaperones, proceed to fold normally – many different molecular chaperones exist, and some have ther functions as well other functions as well » e.g., some also assist with DNA replication, protein assembly, protein transport, etc.
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chaperonins : directly facilitate protein folding g Groin scherichia coli e.g., Gro in Escherichia coli – large, cylindrical macromolecular assemblies formed by 2 oligomeric rings of 7-8 subunits each – a partly folded / misfolded polypeptide is inserted into the cylinder, where it binds the inner wall and folds native nformation (usually the most stable) conformation (usually the most stable) – in an ATP-dependent step, undergoes conformational change, releasing the folded protein
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• misfolded proteins appear to cause a variety of diseases in mammals: – mad cow disease (bovine spongiform encephalopathy) – scrapie (in sheep) – chronic wasting disease (in deer)
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MBB222-lecture8 - most proteins can fold without...

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