Chapter 4.3: Protein Tertiary and Quaternary Structures

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Chapter 4.3Protein Tertiary and Quaternary
Structures

• CHEM 7784
• Biochemistry
• Professor Bensley

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CHAPTER 4.3 Proteins Tertiary and Quaternary
Structures
Todays Objectives - To learn and understand

• The structural hierarchy in proteins (tertiary
  and quaternary structures)
• The structure and function of fibrous proteins
• The structural analysis of globular proteins

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Quiz Question 23

• Fibrous proteins differ from globular proteins in
  that
• fibrous proteins tend to serve structural
  functions, and globular proteins are more likely
  to be enzymes.
• b) fibrous proteins can often contain several
  types of secondary structure, whereas globular
  proteins usually consist largely of a single
  type of secondary structure.
• c) globular proteins are insoluble in water, and
  fibrous proteins are usually soluble.
• d) globular proteins are more likely than
  fibrous proteins to have an elaborate quaternary
  structure.

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Protein Tertiary Structure

• Tertiary structure refers to the overall spatial
  arrangement of atoms in a polypeptide chain or in
  a protein
• Two major classes
• fibrous proteins
• globular proteins

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Proteins with similar 1o structure also have
similar 3o structure
tuna 1 GDVAKGKKTFVQKCAQCHTVENGGKHKVGPNLWGLFGRK
TGQAEGYSYTDANKSKGIVWNyeast 1
GSAKKGATLFKTRCLQCHTVEKGGPHKVGPNLHGIFGRHSGQAEGYSYTD
ANIKKNVWDErice 1 GNPKAGEKIFKTKCAQCHTVDKGAGHKQ
GPNLNGLFGRQSGTTPGYSYSTANKMAVIWEEtuna 61
ETLMEYLENPKKYIPGTKMIFAGIKKKGERQDLVAYLKSATSyeast
61 NNMSEYLTNPKKYIPGTKMAFGGLKKEKDRNDLITYLKKACEric
e 61 NTLYDYLLNPKKYIPGTKMVFPGLKKPQERADLISYLKEATS

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Fibrous Proteins From Structure to Function
Function Structure
Example Tough, rigid, Cross-linked
a-helixes a-keratin hard (nails, horns) Rigid
linker (SS) Tensile strength, Cross-linked
triple-helixes Collagen non-stretching Flexible
linker (Lys-HyLys) (tendons, cartilage) Soft,
flexible Non-covalently held b-sheets non-stretch
y van der Waals interaction Silk fibroin (egg
sac, nest, web)
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Structure of ?-Keratin in Hair
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Structure of Collagen
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Collagen Fibrils
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Silk Fibroin
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Motifs (folds)
Arrangements of several secondary structure
elements
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Motifs Combine to form Domains
Parallel twisted sheet
Alpha/beta barrel
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Quaternary Structure

• Quaternary structure is formed by spontaneous
  assembly of individual polypeptides into a larger
  functional cluster

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Protein Structure Methods X-Ray Crystallography
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Protein Structure Methods Biomolecular NMR