chapter 5 students - From Protein Structure to Function...

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From Protein Structure to Function 1. Hemoglobin and myoglobin: Principles of reversible ligand binding 1. (Antibodies: Principles of specific, high affinity ligand binding) 2. Myosin and actin: Protein activity modulated by ATP 3. Enzymes 1 MCDB310 – Chapter 5: Protein Function
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Ligand Binding usually transient and reversible interaction with others molecule (= ligands) such as metals, hormones often involves “ molecular breathing ” of the protein, i.e. ability to undergo small conformational changes often induces molecular rearrangements in the protein ligand binding sites are - highly conserved - complementary in size, shape, and charge 2 MCDB310 – Chapter 5: Protein Function
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model proteins to study reversible ligand binding Mb: First protein whose structure was solved (1958) very important for oxygen binding in muscle (Mb) and oxygen transport in blood (Hb) metal ions (Fe, Co) are good oxygen binders, but free metal ions are very reactive O 2 binding component in Mb and Hb is heme -protoporphyrine ring with a central Fe 2+ , which reversibly binds oxygen 3 MCDB310 – Chapter 5: Protein Function Myoglobin (Mb) & Hemoglobin (Hb)
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prosthetic group of Mb and Hb incorporated into Hb and Mb during folding responsible for reversible O 2 binding responsible for red color of blood and muscles 4 MCDB310 – Chapter 5: Protein Function Heme
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4 pyrrole rings linked by methene bridges (= protoporphyrine) pyrrole ring X: additional functional groups methene bridge 5 MCDB310 – Chapter 5: Protein Function Heme – Basic Structure
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central Fe 6 MCDB310 – Chapter 5: Protein Function Heme – Structure 2 vinyl groups (buried in protein) 4 methyl groups 2 propionate groups (exposed)
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Fe + + Fe 2+ has 6 coordination sites (4 with N of pyrrole rings, and 2 perpendicular to ring system) Hb: 5 th coordination site is occupied with proximal His 6 th coordination site: O 2 oxyhemoglobin none deoxyhemoglobin CO carboxyhemoglobin 7 MCDB310 – Chapter 5: Protein Function Heme – Iron Coordination
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8 MCDB310 – Chapter 5: Protein Function Heme – Binding of CO vs. O 2 free heme binds C0 10 5 times better than O 2 kinked binding topology in Mb favors O 2 100fold
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Myoglobin (Mb) primarily found in muscle (highly abundant in marine mammals such as whales) single polypeptide (153 aa) with one bound heme very simple oxygen binder: Binds oxygen at high pO 2 , releases it at low pO 2 Mb + O 2 MbO 2 typical globin fold 9 MCDB310 – Chapter 5: Protein Function
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8 helices (A-H) and loops in between 10 MCDB310 – Chapter 5: Protein Function The Globin Fold
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Binding/Association Constant K a Quantitatively describes the affinity of a protein P for its ligand L P + L PL the higher the binding affinity, the higher K a 11 MCDB310 – Chapter 5: Protein Function [L] [P] ] PL [ = a K
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This note was uploaded on 04/05/2009 for the course MCDB 310 taught by Professor Walter during the Spring '09 term at University of Michigan.

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chapter 5 students - From Protein Structure to Function...

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