2009-09-21_-_Lecture_8

2009-09-21_-_Lecture_8 - Biochemistry 461 FS 2009 Michigan...

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Biochemistry 461 FS 2009 Michigan State University Ligand Binding: Myoglobin and Hemoglobin September 21, 2009 Lecture 8 • Loss of protein/enzyme function • Unfolded or misfolded proteins will generally expose hydrophobic surface (nonpolar side chains) to the solvent. • Such a surface can interact with an exposed hydrophobic surface on another protein molecule (of the same or different protein) leading to irreversible denaturation via the formation of aggregates. • In some cases, regular arrays of nonnative proteins, called amyloids , can form. These can be actively detrimental to cellular function and lie at the root of a number of diseases: • Alzheimer’s disease • Prion diseases (scrapie, mad cow, Creutzfeld-Jacob, …) • It is therefore in the cells best interest to quickly isolate and either degrade or refold misfolded proteins as quickly as possible. How does the cell do this? Why is Denaturation Bad? (from previous lecture) 2
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Protein Folding is Cooperative (from previous lecture) Unfolding – there are 2 well-defined states: folded and unfolded • Deform the folded state a little, and it will generally recover back • Deform the folded state too much, and you reach the tipping point: water rushes in, attacks the H-bonds of secondary structure and the whole tertiary structure falls apart Folding – a half-folded protein will generally unfold, not fold • It has too few interactions to hold its shape
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2009-09-21_-_Lecture_8 - Biochemistry 461 FS 2009 Michigan...

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