Lecture 10. Protein function
Tuesday 19 February 2019
Myoglobin: An oxygen-binding protein. Tertiary structure of myoglobin and the heme prosthetic group. Ligand-binding proteins. A general saturation curve for a ligand-binding protein. Hemoglobin: Tertiary and quaternary structure. Cooperative vs. noncooperative ligand binding. Allosteric effects: Homotropic and heterotropic. The Bohr effect and BPG binding. The molecular basis of physiological adaptations and disease.
Reading: Lehninger - Ch.5, pp.157-174.
Summary
Reading summary. §5.1 Reversible binding of a protein to a ligand: Oxygen-binding proteins. Oxygen can bind to a heme prosthetic group. Globins are a family of oxygen-binding proteins. Myoglobin has a single binding site for oxygen. Protein-ligand binding can be described quantitatively. Worked example 5-1: Receptor-ligand binding constants. Protein structure affects how ligands bind. Hemoglobin transports oxygen in blood. Hemoglobin subunits are structurally similar to myoglobin. Hemoglobin undergoes a structural change on binding oxygen. Hemoglobin binds oxygen cooperatively. Cooperative ligand binding can be described quantitatively. Two models suggest mechanisms for cooperative binding. Box 5-1 -Medicine- Carbon monoxide: A stealthy killer. Hemoglobin also transports H+ and C)2. Oxygen binding to hemoglobin is regulated by 2,3-bisphosphoglycerate. Sickle cell anemia is a molecular disease of hemoglobin.
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Myoglobin is a monomeric oxygen-binding protein containing a heme prosthetic group. Myoglobin, whose physiological role is to store or facilitate diffusion of oxygen in muscle, has a hyperbolic oxygen binding curve. The equation for this curve is readily derived from the expression for the oxygen-binding equilibrium and the definition for fractional saturation.