BioChm01-Jan3107Lec7

BioChm01-Jan3107Lec7 - 1 Crystalline proteins often adopt...

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2 Crystalline proteins often adopt nearly the same structure that they have in solution. The strongest example of this is that enzyme crystals retain their enzymatic activity in the crystalline state. Contoured electron density map of a section of a protein. Based on the resolution of the electron density map modeling studies lead to the structure of the molecule. The smaller the ‘value’ of the resolution of the structure the more of the atomic details will be available
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3 Myoglobin was the first protein whose structure was determined by X-ray crystallography (John Kendrew in 1959) Myoglobin is a oxygen binding protein, containing a single heme group, tightly tucked in a hydrophobic pocket. The heterocyclic ring system of heme is a porphyrin derivative containg four pyrrole groups (linked by methene linkages), whose nitrogens coordinate to the central Fe(II). A N-atom from a His residue (His F8) forms the fifth coordination. The sixth ligand is often by an oxygen molecule. The six ligands coordinated to the Fe(II) create an octahedral geometry . In an isolated heme when the Fe(II) is exposed to O 2 It irreversibly converts to Fe(III), and this oxidized form of iron cannot bind oxygen. The protein portion of myoglobin prevents this process and allows the oxygen to bind reversibly to the heme group.
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4 The top picture is a space-filling model The line drawing shows the residues Val and Phe (red asterisks) creating the hydrophobic pocket. The Fe(II) coordinated Oxygen is H-bonded to a His residue. The Val and Phe keep the heme in place and
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BioChm01-Jan3107Lec7 - 1 Crystalline proteins often adopt...

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