2 - Protein structure

Question 1

Give the six hierarchical layers of hair

Answer 1

• Packed dead cells
• Cells packed with macrofibrils
• Microfibrils made with microfibrils that are cemented together by S-rich protein matrix
• Microfibrils composed of 4 protofibrils
• Each protofibrils is composed of a linear series of head-to-tail aligned keratin ‘coiled coils’
• Each coiled coil is a heterodimer of Type I and II alpha-keratin

Question 2

What determines the degree of curliness in hair?

Answer 2

The amount of S cross bridges between microfibrils

Question 3

Describe a coiled-coil

Answer 3

A helix with slightly tighter repeat per turn than alpha helices.

3.5 residues per turn vs. 3.6

Helix is inherently coiled

Question 4

Why is a coiled coil considered a heptad repeat?

Answer 4

Because there are 3.5 residues per turn. Therefore 7 until you’re back at your starting position.

Question 5

What function does the coiled nature of a coiled coil give?

Answer 5

It allows ridges of one helix to insert into grooves of the other

Question 6

Fibrinogen is a 3-4 strand ____ structure. It is cleaved to form fibrin, which has striations __ the length of fibrin.

Answer 6

Fibrinogen is a 3-4 strand coiled-coil structure. It is cleaved to form fibrin, which has striations 1/2 the length of fibrin.

Question 7

Give the structure of collagen.

Answer 7

• Triple helix: three helical polypeptides wound around each other
• Gly-X-Y repeat (each chain)
• Gly is needed to allow triple helix packing
• X: 30% proline
• Y: 33% 4(R)-hydroxyproline (Hyp)

Question 8

What is the most important qualities of collagen?

Answer 8

• Tensile strength for tissue and organs

Question 9

At what parts of collagen’s sequence does it show the most heterogeneity (variability)?

Answer 9

The X and Y parts (not the Gly parts)

There are extremes in conformation for imino rich vs . amino rich regions

Question 10

What is the equivalent for elastin in insects?

Answer 10

Resilin (for motility)

Question 11

Give the basic structure of human tropoelastin

Answer 11

Alternating hydrophobic and cross linking domains

Question 12

How does resilin store energy when it is bent by muscle in insects?

Answer 12

Energy input converts disordered elastic domains to beta-turns, allowing energy storage.

Question 13

True or false. Spider silks are stronger and tougher than any synthetic material?

Answer 13

True

Question 14

What gives the different spider silks their differing properties?

Answer 14

Highly variable primary structure

Question 15

What did Raman spectroscopy reveal about spider silks?

Answer 15

Their secondary structures

Eg. alpha and beta sheet content differs

One gland produces heterogeneous and disordered silk

Question 16

What are the two predominant theories in silk building?

Answer 16

• Micelle theory (physical shear is exerted on micelles, inducing beta sheet formation)
• Liquid crustal theory (Producing a liquid crystalline form and squeezing it into oriented beta sheets.

Question 17

In spider silk, strength comes from ____ domains. Elasticity from ____ regions.

Answer 17

Strength: beta-sheet domains

Elasticity: disordered regions

Alpha helices may make it more ‘tough’

Question 18

Outline the differences in glycine/proline content for fibrinigous and elastic protein domains.

Answer 18

Fibrinigous domains: Low gly, low pro

Elastic: High gly, moderate pro

Question 19

What are motifs?

Answer 19

In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a supersecondary structure, which also appears in a variety of other molecules. Motifs do not allow us to predict the biological functions: they are found in proteins and enzymes with dissimilar functions.

They lack a (full) hydrophobic core. Domains are the simplest self contained units. Domains (folds) are made up of motifs

Question 20

True or false? Nature is conserved when it comes to folding proteins?

Answer 20

True. There are about 1200 known folds, but half of the known structures fall into only 20 fold groups!

Question 21

Fibrous proteins are to ___ structure as globular proteins are to ___ structure

Answer 21

Fibrous proteins are to ‘secondary’ structure as globular proteins are to ‘tertiary’ structure

Question 22

What is the hallmark of elastin assembly?

Answer 22

Coacervation mechanism

This where colloidal elastin droplets are electrostatically attracted to form branched fibrillar structures.

Fibrillin and fibulin can associate with coalesced species to aid in structure and rigidity.

Question 23

What is a major function of resilin in flying insects?

Answer 23

It is stretched by muscle, converting energy for spring like release that saves more than 10% of energy per stroke

Question 24

Give the basic conformation of each exon of resilin

Answer 24

Exon I: disordered when relaxed

Exon II: Chitin binding domain, alpha helical

Exon III: Disordered when relaxed