Bonev - Structural proteins

Question 1

What are some characteristics found in structural proteins and not found in globular proteins?

Answer 1

• Long, filamentous
• Insoluble
• Contain unusual amino acids
• Often contain cross-linked polypeptide chains (polypeptides are covalently linked together to give a more stable structure)

Question 2

What happens to keratin when epithelial cells die?

Answer 2

Keratin is retained within the cells and produced

Question 3

Where is a-keratin predominantly found?

Answer 3

Outermost layer of skin, horns, hooves, and hair

Question 4

Where are b-keratins found?

Answer 4

Feathers, scales

Question 5

What type of structure does keratin form?

Answer 5

Forms alpha helical structures in a right-handed way

Question 6

Which way does it supercoil though?

Answer 6

Left-handed. Right-hand coils supercoil in a left-hand sense.

Question 7

How many residues are present per turn in the protofilaments?

Answer 7

Two coiled right-hand helices with 3.5 residues per turn. Alpha helix has 3.6 residues per turn.

Question 8

What is the pitch?

Answer 8

0.51nm

Question 9

What is the pitch for the LH supercoiling?

Answer 9

21nm

Question 10

8 protofibrils form a keratin microfilament. Cysteine can also form disulfide bonds with other cysteine molecules which stabilises the entire structure.

Question 11

What type of helical wheel is present in the keratin structure?

Answer 11

Heptad helical wheel

Question 12

Why is it important that Leu, Ile, Ala are found at ‘a’ and ‘d’?

Answer 12

These are hydrophobic causing a hydrophobic surface, allowing interaction between the two coils, making it more stable

Question 13

What happens if Arg and Lys (both positive) are found at opposite positions of the heptad wheel (at g and e)?

Answer 13

They will form a salt bridge with negative residues to stabilise the elctrostatic interactions

Question 14

Where is collagen found?

Answer 14

In connective tissue like bones, cartilage, ligaments, tendons, and skin

Question 15

Which amino acid comprises 33% of collagen?

Answer 15

Glycine

Question 16

Why is tryptophan not found in collagen?

Answer 16

Because it has bulky sidechains which would disrupt the tight packaging and stability of the tight triple helix

Question 17

How many amino acids make each of the three chains in collagen?

Answer 17

1000 amino acids

Question 18

What handedness are they each?

Answer 18

Right-handed

Question 19

They are 300nm long, 1.4nm in diameter, 285kDa in molecular weight

Question 20

Why does collagen have proline present in its structure?

Answer 20

Because it is unable to form hydrogen bonds

Question 21

Why does collagen not want hydrogen bonding as much as other structures?

Answer 21

Because a reduced amount of hydrogen bonding leads to increased flexibility

Question 22

Which amino acid is present in collagen so that there is some hydrogen bonding for stability?

Answer 22

Hydroxyproline

Question 23

How does hydroxyproline work?

Answer 23

It serves as a hydrogen bond acceptor and raises the melting temperature from 24ºC to 40-60ºC

Question 24

Helical pitch is around 0.95nm with 3.3 residues per turn

Question 25

Why is it important to have glycine in the structure?

Answer 25

It faces inwards and has no sidechains. This gives it a more tight and compact structure.

Question 26

What is the difference between collagen and tropocollagen?

Answer 26

Tropocollagen is each of the individual strands but collagen is the three strands together

Question 27

What is the higher order of organisation present in tropocollagen? (staggering)

Answer 27

Staggered alignment of tropocollagen, 64nm staggering with 40nm gaps

Question 28

There is some covalent cross-linking within individual helices, as well as between helices

Question 29

An allysine and lysine can react together to form what?

Answer 29

Schiff base with no chemically active group

Question 30

Why is hydroxylation of lysine and proline needed as a post-translational modification in collagen formation?

Answer 30

To enable the possibility of hydrogen bonding to increase stability like the melting point increasing

Question 31

Why is glycosylation needed?

Answer 31

Serine for example needs to be glycosylated to make it more soluble and facilitate exocytosis

Question 32

Which amino acids make up collagen?

Answer 32

Glycine, proline, alanine, hydroxyproline, and others

Question 33

Where does a mutation tend to occur in collagen?

Answer 33

Glycine

Question 34

What does this lead to?

Answer 34

Collagen misfolding, increased Lys hydroxylation, improper processing of the protofilaments by enzymes and chaperones, and weakening of the collagen protofilaments

Question 35

Where is elastin found?

Answer 35

Connective tissue like arterial walls and ligaments

Question 36

What is it mainly composed of?

Answer 36

Gly 33%, 22% Ala, 14% Val, 11% Pro

Question 37

How can elastin form a mesh-like structure to make it more stable and compact?

Answer 37

Lysine has its sidechains form isodesmosine and desmosine. These enable flexibility and strength in these covalent structures.

Question 38

Fibrillin is found in microfibrils which contribute alongside elastin and collagen to the structure of the extracellular matrix. What is unique about fibrillins?

Answer 38

They have 47 Epidermal Growth Factors, 43 of which bind to calcium

Question 39

What is Marfan's syndrome a result of and what does this prevent?

Answer 39

Mutations found in the Epidermal Growth Factors and this reduces calcium binding

Question 40

What does this lead to?

Answer 40

Extensive growth of organism, extended vasculature

Question 41

Where is fibroin secreted from?

Answer 41

Insects and arachnids

Question 42

What is the amino acid content?

Answer 42

Gly 45%, Ala 30%

Question 43

What is the main secondary structure found in fibroin?

Answer 43

Antiparallel beta sheets

Question 44

They have lots of glycine so there are no side chains. The sheets can slide against each other which makes it very flexible. It is an exceptionally strong polymer.

Question 45

If all these sheets come together, what type of structure is formed?

Answer 45

Crystalline domains

Question 46

Polyalanine motifs are repeated throughout the structure, what does this give it?

Answer 46

A lot of strength and rigidity

Question 47

What holds this crystalline structure together?

Answer 47

Sericins

Question 48

Which enzyme converts lysine to allysine in collagen?

Answer 48

Lysyl oxidase

Question 49

What is the purpose of allysine being produced in collagen?

Answer 49

It can form cross-bridges with other allysine which stabilises the structure further

Question 50

Which Schiff base is produced when allysine reacts with a lysine?

Answer 50

Lysinonorleucine

Question 51

Why is this important in collagen?

Answer 51

Provides structural stability