CH 4 Protein Structure and Function

CH 4 Protein Structure and Function - 9/14/09 Chapter 4...

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9/14/09 1 Chapter 4 Protein Structure and Function Objectives Understand the different levels of protein structure Understand the basis for protein-protein and protein-ligand interactions Understand the relationship between protein structure and enzymatic catalysis Be familiar with common mechanisms for controlling enzyme activities
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9/14/09 2 Levels of Protein Structure • Primary Amino acid sequence • Secondary Stable folding patterns within a polypeptide • Tertiary Full three-dimensional conformation • Quaternary Complete structure of a complex formed between more than one polypeptide chain Primary Structure Amino acid sequence • Amino acids are joined together through condensation reactions to form peptide bonds • The order of amino acids in a linear polypeptide “string” is specific, and this sequence ultimately determines the three-dimensional structure of the protein • Proteins have structural polarity
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9/14/09 3 There is an error in this figure (from 2 nd Edition)! Protein folding As a polypeptide is being synthesized, it is very flexible. In principle, it could fold in many different ways. Most proteins fold into a stable three- dimensional molecule shortly after (and even during) synthesis Unstable folding leads to degradation or aggregation. What constrains protein folding?
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9/14/09 4 Protein folding Constrained by the formation of many weak noncovalent bonds • Polypeptide backbone • Amino acid side chains Ionic bonds Hydrogen bonds Hydrophobic interactions Van der waals attractions A single noncovalent bond may be weak, but many of them together form a strong arrangement
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9/14/09 5 Hydrophobic interactions constrain protein folding Protein conformation is determined by its sequence (minimized free energy) H 2 N-C-NH 2 O II
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9/14/09 6 Christian B. Anfinsen (1916-1995) Science 125:691 (1957) Reductive Cleavage of Disulfide Bridges in Ribonucleases
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CH 4 Protein Structure and Function - 9/14/09 Chapter 4...

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