1. Fibrous Proteins Examples 1. a-keratins 2. Silk Fibroin 3. Collagen
Hair, nails, horns, skin
2. Silk Fibroin
3. Collagen
4. Elastin
Saw Varsity’s a-keratins off

2. Amino Acid Composition of Fibrous Proteins
-Keratin
(Wool)
Fibroin
(Silk)
Collagen
(Tendon)
Elastin
(Aorta)
Gly
Ala
Ser
Glu + Gln
Cys tr.
Pro
Arg
Leu
Thr
Asp + Asn
Val
Tyr
Ile
Phe
His tr.
Met tr.
Trp tr.

3. -Keratin

4. Keratin: an Intermediate Filament Protein
What’s in Hair
and Wool?

5. Collagen Intramolecular Crosslinks Intermolecular Crosslinksb a’
Gly-X-Y a
Left hand
-helix
X=Pro
Y=HO-Pro
Intermolecular Crosslinks
Quarter Stagger

6. ELASTIN Property of Resilience 4-way Stretch Aorta Lung
Ligamentum Nuchae

7. Tertiary Structure Overall Shape (applies mainly to globular proteins)
Alpha helix
Beta structure
Structural Motifs
Beta barrel
Beta-alpha-beta

8. Globular Protein Molecules
3-Dominant Structural Features
Helix a
Beta Sheet
Turns or loops
Typical Protein
Packs
Framework
Connects

9. Rules Governing Protein Folding
Can we predict how a protein will fold on the
basis of amino acid sequence data alone?
1. Globular Proteins have a defined outside and inside
Hydrophobic buried inside
Hydrophilic outside

10. Folding and Biological Activity
Enzyme Active Site Z X Y X Z Y
Random Coil
Folded
Denatured
Biologically Active

11. TURNS (on Surfaces) Reverse direction abruptly
Beta Bends or Turns (4 residues to execute sharp turn)
H-bonding between carbonyl residue1 and
amide N on residue 3.
Glycine not in loop (Type I turn)
Glycine in loop
(Type II turn)
Gamma (very tight turn)
Proline in loop, bonding between 1 and 2
Tight Turn

12. Reverse Turn in Polypeptides
Glycine
H-bond between
1 and 4
Twice more common than type 2

13. Chou-Fasman Rule for Predicting Secondary Structure
Propensity
Helix
Beta Sheet
Beta Turn

14. Protein Folding Mystery
To fold a protein is negative entropy with
respect to the protein. You go from a disordered
to an ordered state.
Folding is away from a natural tendency
to exist in a random state?
Where is the energy driving protein folding?
ANSWER IN TEXTBOOK

15. ANSWER DSTotal = DSsys - DSsurround ORGANIZED WATER N C Folded N C
Unfolded
ORGANIZED WATER
DSTotal = DSsys - DSsurround

16. QUATERNARY STRUCTURE SUBUNIT STRUCTURE Multisubunit Proteins HOMODIMER
HETERODIMER

17. WEAK FORCES IN PROTEIN

18. Hydropathic Index +
hydrophobic _
hydrophilic

19. Determining Hydropathic Index
Sum 1-9 (window)
Sum 2-10
Sum 3-11
Sum 4-12
Sum 5-13
Sum 6-14
(-)
(+)