lecture_13 - Protein Function Globins and Antibodies...

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Protein Function Globins and Antibodies 3/10/2003
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Hemoglobin and Myoglobin Because of its red color, the red blood pigment has been of interest since antiquity. First protein to be crystallized - 1849. First protein to have its mass accurately measured. First protein to be studied by ultracentrifugation. First protein to associated with a physiological condition. First protein to show that a point mutation can cause problems. First proteins to have X-ray structures determined. Theories of cooperativity and control explain hemoglobin function
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The structure of myoglobin and hemoglobin Andrew Kendrew and Max Perutz solved the structure of these molecules in 1959 to 1968. The questions asked are basic. What chemistry is responsible for oxygen binding, cooperativity, BPG effects and what alterations in activity does single mutations have on structure and function. Myoglobin: 44 x 44 x 25 Å single subunit 153 amino acid residues 121 residues are in an a helix. Helices are named A, B, C, …F. The heme pocket is surrounded by E and F but not B, C, G, also H is near the heme. Amino acids are identified by the helix and position in the helix or by the absolute numbering of the residue.
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The Backbone structure of Myoglobin 4
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The Heme complex in myoglobin
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Hemoglobin Spherical 64 x 55 x 50 Å two fold rotation of symmetry α and β subunits are similar and are placed on the vertices of a tetrahedron. There is no D helix in the α chain of hemoglobin. Extensive interactions between unlike subunits α 2- β 2 or α 1- β 1 interface has 35 residues while α 1- β 2 and α 2- β 1 have 19 residue contact . Oxygenation causes a considerable structural conformational change
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Quaternary structure of deoxy- and oxyhemoglobin T-state R-state
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Oxygenation rotates the α 1 β 1 dimer in relation to α 2 β 2 dimer about 15° The conformation of the deoxy state is called the T state The conformation of the oxy state is called the R state individual subunits have a t or r if in the deoxy or oxy state. What causes the differences in the conformation states? It is somehow associated with the binding of oxygen, but how?
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2 binding to Hb arises from the effect of the ligand-binding state of one heme on the ligand-binding affinity of another. The Fe iron is about 0.6 Å out of the heme plane in the deoxy state. When oxygen binds it pulls the iron back into the heme plane. Since the proximal His F8 is attached to the
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lecture_13 - Protein Function Globins and Antibodies...

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