Fibrous Proteins Examples 1. a-keratins 2. Silk Fibroin 3. Collagen

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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

Amino Acid Composition of Fibrous Proteins -Keratin (Wool) Fibroin (Silk) Collagen (Tendon) Elastin (Aorta) Gly 8.1 44.6 32.7 32.3 Ala 5.0 29.4 12.0 23.0 Ser 10.2 12.2 3.4 1.3 Glu + Gln 12.1 1.0 7.7 2.1 Cys 11.2 0 0 tr. Pro 7.5 0.3 22.1 10.7 Arg 7.2 0.5 5.0 0.6 Leu 6.9 0.5 2.1 5.1 Thr 6.5 0.9 1.6 1.6 Asp + Asn 6.0 1.3 4.5 0.9 Val 5.1 2.2 1.8 12.1 Tyr 4.2 5.2 0.4 1.7 Ile 2.8 0.7 0.9 1.9 Phe 2.5 0.5 1.2 3.2 His 0.7 0.2 0.3 tr. Met 0.5 0 0.7 tr. Trp 1.2 0.2 0 tr.

-Keratin

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

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

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

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

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

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

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

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

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

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

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

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

QUATERNARY STRUCTURE SUBUNIT STRUCTURE Multisubunit Proteins HOMODIMER HETERODIMER

WEAK FORCES IN PROTEIN

Hydropathic Index + hydrophobic _ hydrophilic

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