Introduction to Proteins

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Introduction to Proteins
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Proteins(Amino Acids)
Only 20 naturally-occurring amino acids Only
linear structures
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Functions of Proteins I

• Catalysts and Metabolic Regulation Enzymes
• Protection
• Serum antifreeze proteins
• Blood coagulation
• Antibodies
• Membrane Transport Nutrients
• Signal Transduction Cell Surface Receptors
• Structural Support Collagen

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Functions of Proteins II

• Coordinated Motion Muscle Contraction
• Genetic Regulation DNA Binding Proteins
• Transport Hemoglobin
• Generation and Transport of Nerve Impulses
• Nutrient Storage
• Seed proteins
• Casein in milk

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Function of proteins largely due to properties of
constituent amino acids
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Structure of Proteins

• Simple Proteins
• Conjugated Proteins
• Cofactors
• Prosthetic Groups
• Oligomeric Proteins (more than one polypeptide
  chain)

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Conjugated Proteins
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Oligomeric Proteins(more than one polypeptide
chain)

• Subunits held together by covalent or
  non-covalent linkages
• Identical subunits
• Non-identical subunits
• Covalent linkages are not peptide bonds

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Classes of Shape

• Globular Proteins
• Spherical
• Soluble
• Dynamic Function e.g. catalysis (enzymes)
• Fibrous Proteins
• Rod-like
• Insoluble
• Structural

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Levels of Structure

• Primary Structure amino acid sequence
• Secondary Structure backbone structure
  (backbone atoms)
• Tertiary Structure three dimensional folding
  (side chain atoms)
• Quaternary Structure structural relations
  between subunits of oligomeric proteins

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Conformation of Proteins(overall three
dimensional structure of a protein)

• Conformation is a property of amino acid sequence
• Chaperones assist in the proper folding of
  proteins

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Supramolecular Structures
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The Theoretical Possibilities for Polypeptides
are Unlimited

• Actual Polypeptides are Somewhat Limited in Size
  and Composition

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Bovine Insulin
Figure 5-1
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Composition of Some Proteins
Table 5-1
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Protein Purification and Analysis

• Purifying a Protein Requiresa Strategy

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Physical Characteristics Distinguishing Proteins
Page 97
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Fractionation by Salting Out
Figure 5-5
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Isoelectric Points of Several Common Proteins
Table 5-2
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Ion Exchange Chromatography
Figure 5-6
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Gel Filtration Chromatography
Figure 5-7
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Affinity Chromatography
Figure 5-8
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SDS-PAGE
Figure 5-9
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Molecular Mass and Electrophoretic Mobility
Figure 5-10
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Two-Dimensional Gel Electrophoresis
Figure 5-11
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Primary Structure Determination
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Strategy

• Purification of protein to homogeneity
• Prepare protein for sequencing
• Sequence polypeptide chains
• Organize completed structure
• Nucleic Acid Sequencing

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Prepare Protein for Sequencing

• End Group Analysis How many different subunits
• Cleavage of disulfide bonds
• Separation and purification of the polypeptide
  chains
• Amino acid composition

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Sequence Polypeptide Chains

• Specific peptide cleavage reactions
• Separation and purification of peptide fragments
• Sequence determination

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Organize Completed Structure

• Ordering peptide fragments
• Assignment of disulfide bond positions
• Determine position of amides