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Chapter 4.3:Protein Tertiary and
Quaternary StructuresCHEM 7784
BiochemistryProfessor Bensley
CHAPTER 4.3 Proteins: Tertiary and Quaternary
Structures
– The structural hierarchy in proteins (tertiary and quaternary structures)
– The structure and function of fibrous proteins
– The structural analysis of globular proteins
Today’s Objectives - To learn and understand:
Quiz Question 23
Fibrous proteins differ from globular proteins in that:a)fibrous proteins tend to serve structural functions, andglobular 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.
• 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
Protein Tertiary Structure
Proteins with similar 1o structure also have similar 3o structure
tuna 1 GDVAKGKKTFVQKCAQCHTVENGGKHKVGPNLWGLFGRKTGQAEGYSYTDANKSKGIVWNyeast 1 GSAKKGATLFKTRCLQCHTVEKGGPHKVGPNLHGIFGRHSGQAEGYSYTDANIKKNVWDErice 1 GNPKAGEKIFKTKCAQCHTVDKGAGHKQGPNLNGLFGRQSGTTPGYSYSTANKMAVIWEE
tuna 61 ETLMEYLENPKKYIPGTKMIFAGIKKKGERQDLVAYLKSATSyeast 61 NNMSEYLTNPKKYIPGTKMAFGGLKKEKDRNDLITYLKKACErice 61 NTLYDYLLNPKKYIPGTKMVFPGLKKPQERADLISYLKEATS
Fibrous Proteins: From Structure to Function
Function Structure Example
Tough, rigid, Cross-linked -helixes -keratinhard (nails, horns) Rigid linker (S—S)
Tensile strength, Cross-linked triple-helixes Collagennon-stretching Flexible linker (Lys-HyLys)(tendons, cartilage)
Soft, flexible Non-covalently held -sheetsnon-stretchy van der Waals interaction Silk fibroin(egg sac, nest, web)
Structure of -Keratin in Hair
Structure of Collagen
Collagen Fibrils
Silk Fibroin
Motifs (folds)
Arrangements of several secondary structure elements
Motifs Combine to form Domains
Alpha/beta barrel
Parallel twisted sheet
Quaternary Structure
• Quaternary structure is formed by spontaneous assembly of individual polypeptides into a larger functional cluster
Protein Structure Methods: X-Ray Crystallography
Protein Structure Methods: Biomolecular NMR