Tertiary Structure

What are characteristics of globular proteins?

Create maximum internal bonds and minimize solvent contact

What are characteristics of fibrous proteins?

Create maximun intermolecular bonds and maximize molecule to molecule contact

Where are membrane proteins found?

Embedded within a lipid-bilayer

How do proteins fold?

To form the most stable structures

Where does stability arise from?

Formation of large numbers of intramolecular hydrogen bonds, reduction in the surface area accessible to solvent that occurs upon folding

Are fibrous proteins soluble or insoluble?

Insoluble

What type of protein is mechanically strong?

Fibrous proteins

What are examples of fibrous proteins?

a-keratin, b-keratin, fibrin, collagen

What does keratin contain?

Macrofibrils and microfibrils

What structure composes a-keratin?

Left-handed coiled coil

What is the coiled coil?

Bundle of a-helices wound into a superhelix

What composes an elongated left-handed superhelix?

Two right-handed a-helices that intertwine

Where is fibroin and B-keratin found?

In silk fibers and bird feathers

What sequence is found in B-keratin?

Gly-X-Gly-X.. (X-Ala or Ser)

What is fibrinogen?

Extracellular matrix protein that mediates platelet aggregation at the site of injury

Is fibrinogen soluble or insoluble?

It is a soluble protein that becomes insoluble fiber

What happens when fibrino-peptides are cleaved by thrombin?

Forms a fibrin which forms dimers by stacking in an antiparallel fashion that leads to fibrin polymer

What is the proposed model for fibrin?

N-terminal of all three chains of fibrin interact with another n-terminal to form a long rod

Where is collagen found?

Bone, teeth, cartilage, tendon, ligament, skin, blood vessel

What is the most abundant protein of vertabrates?

Collage

What is the typical amino acid composition?

Gly-Proline-Hydroxyproline

What is width of collagen?

14 A

What is length of collagen?

3000 A

How are a-keratin polypeptides formed?

Form closely associated pairs of a-helices twisted into a left handed coil

How is an elongated right-handed superhliex formed?

Three left-handed helices intertwine to form this

What are functions of globular proteins?

Enzymes, transport proteins, antibodies, cell surface proteins, integral membrane proteins, virus coat proteins, storage proteins, DNA binding proteins

What are the functions of cavities in globular proteins?

Provide flexibility for proteins and facilitate conformation changes and protein dynamics

What are the four structural classes of globular proteins?

1. a proteins

2. B proteins

3. a/B proteins

   1. a+B proteins

What are a proteins?

a helices predominate

What are B proteins?

In which B sheets predominate

What are a/B proteins?

Helices and sheets are intermingled

What are a+B proteins?

Contain a-helical and B-sheet domains

What does flexibility allow for?

Ligand binding, enzyme catalysis, enzyme regulation

How does water stabilzie protein structure?

Polar backbone and side chain groups on the protein surface make H bodns with solvent water

What is the basis for enzyme-substrate interactions?

Cell surface that is a complex landscape of different structural elements

What is a ranom coil?

Segments of protein that are not helices or sheets