1. Chapter 4.3: Protein Tertiary and Quaternary Structures CHEM 7784 Biochemistry Professor Bensley

2. 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:

3. Quiz Question 23 Fibrous proteins differ from globular proteins in that: a)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.

4. 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

5. Proteins with similar 1 o structure also have similar 3 o structure tuna 1 GDVAKGKKTFVQKCAQCHTVENGGKHKVGPNLWGLFGRKTGQAEGYSYTDANKSKGIVWN yeast 1 GSAKKGATLFKTRCLQCHTVEKGGPHKVGPNLHGIFGRHSGQAEGYSYTDANIKKNVWDE rice 1 GNPKAGEKIFKTKCAQCHTVDKGAGHKQGPNLNGLFGRQSGTTPGYSYSTANKMAVIWEE tuna 61 ETLMEYLENPKKYIPGTKMIFAGIKKKGERQDLVAYLKSATS yeast 61 NNMSEYLTNPKKYIPGTKMAFGGLKKEKDRNDLITYLKKACE rice 61 NTLYDYLLNPKKYIPGTKMVFPGLKKPQERADLISYLKEATS

6. Fibrous Proteins: From Structure to Function Function Structure Example Tough, rigid,Cross-linked  -helixes  -keratin hard (nails, horns)Rigid linker (S—S) Tensile strength,Cross-linked triple-helixes Collagen non-stretchingFlexible linker (Lys-HyLys) (tendons, cartilage) Soft, flexibleNon-covalently held  -sheets non-stretchyvan der Waals interactionSilk fibroin (egg sac, nest, web)

7. Structure of  -Keratin in Hair

9. Structure of Collagen

10. Collagen Fibrils

11. Silk Fibroin

13. Motifs (folds) Arrangements of several secondary structure elements

14. Motifs Combine to form Domains Alpha/beta barrel Parallel twisted sheet

15. Quaternary Structure Quaternary structure is formed by spontaneous assembly of individual polypeptides into a larger functional cluster

16. Protein Structure Methods: X-Ray Crystallography

18. Protein Structure Methods: Biomolecular NMR