lec02 - MIT OpenCourseWare http:/ocw.mit.edu 7.88J Protein...

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MIT OpenCourseWare http://ocw.mit.edu 7.88J Protein Folding Problem Fall 2007 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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Lecture Notes - 2 7.24/7.88J/5.48J The Protein Folding Problem Handouts: An Anfinsen paper Reading List Anfinsen Experiments The Problem of the title refers to how the amino acid sequence of a polypeptide chain determines the folded three-dimensional organization of the chain: Does the sequence determine the structure?? Protein Denaturation Emergence of the Problem Ribonuclease A Refolding of ribonuclease in vitro. A. Protein Denaturation/Inactivation One of the features that identified proteins as distinctive polymers was 1) Unusual phase transition in semi purified proteins When exposed to relatively gentle conditions outside the range of physiological heat pH salt organic solvents, e.g. alcohols Lets consider the familiar transition I mentioned last week; Heat denaturation; cooking the white of an egg Acid denaturation; Milk turning sour Macroscopic changes in bulk solution; scatters visible light, increase in viscosity - white of egg: >>heat; opaque, hard; cool down; no change: Coagulation, Aggregation, precipitation, denaturation: One of the components is egg white lysozyme: activity assay; hydrolysis of bacterial cell walls: Activity remaining vs. temperature on same axes This transition: is Denaturation. These transitions were in general found to be irreversible: activity was not recovered upon cooling: Historically the study of the folding and unfolding of proteins emerged from trying to understand this unusual change of state or phase transitions.
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B. Emergence of the Protein Folding Problem In the period 1958-1960, the first structure of a protein molecule - myoglobin, the oxygen binding protein of muscle - was solved by John Kendrew in 1958, followed soon after by the related tetrameric red blood cell oxygen binding protein, hemoglobin, solved by Max Perutz, both of the British Medical Research Council Labs in Cambridge, U.K. “When the folding of the hemoglobin chain emerged from the model building process, it was shocking. The crystallographers expected each molecule to have high internal symmetry. In fact as Kendrew said, myoglobin is almost nothing but a complicated set of helical rods sometimes going straight for a distance then turning a corner and going off in a new direction;.much more complicated and irregular than most of the early theories of the structure of proteins had suggested.” What’s so surprising; Well like the epicycles every educated person knew that heavenly movements had to be circles; When Kepler showed that orbits were elliptical - a radical departure. Same with proteins; assumed without even being aware, highly regular, formed
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This note was uploaded on 11/11/2011 for the course BIO 7.344 taught by Professor Bobsauer during the Spring '08 term at MIT.

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lec02 - MIT OpenCourseWare http:/ocw.mit.edu 7.88J Protein...

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