Chapter5_BCH461

Chapter5_BCH461 - 9/15/09 1 Chapter 5 Protein function...

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Unformatted text preview: 9/15/09 1 Chapter 5 Protein function Outline Reversible binding of a protein to a ligand: oxygen-binding proteins (Myoglobin & Hemoglobin) Complementary interaction between proteins and ligands: The immune system and immunoglobulins (antibody) Protein interactions modulated by chemical energy: Actin, Myosin, and molecular motors. 9/15/09 2 Intro of key points Proteins are dynamic molecules whose functions depend on interactions with other molecules that can cause conformational change of proteins. The function of many proteins involve the reversible binding of other molecules. A molecule bound reversibly by a protein is called a ligand. Protein-ligand interaction is specific. The binding of a protein and ligand is often coupled to a conformational change in the protein that makes the binding site more complementary to the ligand, permitting tighter binding. The structrual adaptation that occurs between protein and ligand is called induced fit. In a multisubunit protein, a conformational change in one subunit often affects the conformation of other subunits. Interaction between ligands and proteins may be regulated by additional ligand. Hemoglobin and Myoglobin: Paradigms of Protein Structure and Function 9/15/09 3 Oxygen Transport and Storage Myoglobin: a monomeric protein Myoglobin serves as an oxygen storage protein primarily in muscle tissue. It contains one binding site for one O 2 molecule. This binding site is a heme group. 9/15/09 4 More on Myoglobin 1. A globular protein in vertebrate muscle . 2. The first protein whose structure was determined by X-ray crystallography (John Kendrew, 1959). 5. 153 residue monomeric protein containing 8 a helices, A to H , connected by short peptide links, AB, CD, EF, etc. 6. It contains one binding site for one O 2 molecule. This binding site is a heme group that is tightly wedged between E and F helix. 8 -helix, A-H Function of Myoglobin Major role is to facilitate oxygen diffusion in muscle . It increases the effective solubility of O 2 in muscle cells. It also serves as oxygen storage in aquatic mammals, whose myoglobin concentration are around 10-fold greater than that in terrestrial mammals. (sperm whale myoglobin) Neuroglobin, myoglobin-like protein found in brain may be essential for boosting O 2 concentration in brain tissues. (Brain, 2% mass of human body, consumes 20% of the available oxygen. ) 9/15/09 5 What is a heme group? Heme consists of a complex organic ring structure, protoporphyrin, to which is bound a single iron atom in ferrous (Fe 2+ ) state. The iorn atom has six coordination bonds, four to nitrogen atoms that are part of the flat porphyrin ring and two perpendicular to the porphyrin....
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Chapter5_BCH461 - 9/15/09 1 Chapter 5 Protein function...

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