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