SFP13: Structural Proteins

Question 1

What are general characteristics of structural proteins?

Answer 1

• Long, filamentous
• Generally, insoluble
• Contain unusual amino acids
• Often contain cross-linked polypeptide chains

Question 2

Name some extracellular structural proteins

Answer 2

• Keratin
• Collagen
• Elastin
• Resilin
• Fibrillin
• Fibrin
• Spidroin

Question 3

Name cellular structural proteins

Answer 3

Filamentous muscle proteins

Cytoskeleton proteins

Question 4

What three components make up alpha-keratin?

Answer 4

Glutamic acid/ glutamine
Cystine
Serine

Question 5

What are characteristics of alpha-keratins?

Answer 5

Coiled-coil; each stand is a distorted right handed alpha-helix

Double alpha-helical coiled-coil; left handed supercoiling

Question 6

What are characteristics of beta-keratins?

Answer 6

Extended chains

Question 7

What organisation structure does chain packing in alpha keratin take?

Answer 7

Heptane organisation, partial unwinding of the helix

Question 8

Components of protofilaments:

Answer 8

Two coiled RH helices with 3.5 residues per turn (3.6 in alpha-helices)
0.51nm pitch (0.54nm alpha helix)
21nm pitch LH supercoiling

Question 9

What are protofibrils

Answer 9

Two pairs of coiled coils

Question 10

How many protofibrils form each keratin microfibril?

Answer 10

Eight

Question 11

How do cysteine residues stabilise the keratin structure?

Answer 11

They engage in cystine bridges to stabilise the structure through covalent interactions

Question 12

What are the common residues at positions a and d?

Answer 12

Leu, Ile, Ala

Question 13

What residues are often found in positions e and g?

Answer 13

Glu and Gly

Question 14

What residues are often found in position g?

Answer 14

Arg and Lys

Question 15

How does heptane organisation work?

Answer 15

A-C, C-E etc, in the heptane shape

Question 16

What do e and g have sticking out?

Answer 16

Side chains that can be positively or negatively charged

Question 17

Why might the heptane organisation structure have hydrophilic side chains?

Answer 17

To allow it to be in aqueous solution

Hydrophobic core

Question 18

What is collagen a major component of?

Answer 18

Connective tissue… skin, tendons,cartilage, ligaments and bone

Question 19

What is the characteristic repeat motif of collagen?

Answer 19

-G-X-Y-

Where G is glycine

Question 20

What is type 1 collagen?

Answer 20

Type 1: tendons, ligaments, bones, two A1 chains and one a2 chain (two are the same, one is different)

Question 21

What is type 2 collagen?

Answer 21

Cartilage, three A1 chains (all three are the same)

Question 22

What is the helical pitch of collagen?

Answer 22

0.95nm (3.3 residues per turn at 0.286nm per residue)

Question 23

Why does proline prevent formation of many hydrogen bonds?

Answer 23

Proline does not have an amino group that can dissipate into hydrogen bond formation

Question 24

What role does hydroxyproline play in collagen?

Answer 24

Serves as a hydrogen bond acceptor and raises the melting temperature from 24 degrees to over 40 degrees

Question 25

Why does Gly lining the interior of the triple helix, allow for tight packing?

Answer 25

no side chains

Question 26

Where do bulkier side chains position themselves?

Answer 26

On the outer edges of the helices

Question 27

How often is a glycine reside present and why?

Answer 27

Glycine is present every third residue to allow for the tight packing (no side chains)

Question 28

What structure does tropocollagen take?

Answer 28

Triple-stranded (three separate chains) intertwined right-handed helical structure (not alpha-helical)

Question 29

What is posttranslational cross linking (modification)

Answer 29

Collagens cross-link extensively post-translation

Question 30

What does Schiff base formation create?

Answer 30

Lysinonorleucine

Question 31

What are two posttranslational modifications of collagens?

Answer 31

- Hydroxylation of Pro and Lys | - Glycosylation

Question 32

Name four disorders associated with collagen defects?

Answer 32

- Osteogenesis imperfecta - Osteoporosis - Ehlers-Danlos syndrome - joint hyper mobility, skin extensibility, vascular fragility - Familial aortic aneurism (over flexibility of major blood vessels, causing a rupture)

Question 33

Where is elastin found?

Answer 33

Arterial walls and ligaments

Question 34

What is elastin?

Answer 34

Yellow elastic connective tissue

Question 35

What is fibrillin?

Answer 35

Fibrillin is a protein from the micro fibrils, which contribute to the structure of the extracellular matrix together with collagen.

Question 36

Where are microfibrils abundant?

Answer 36

Microfibrils are abundant in skin, blood vessels, tendons

Question 37

What does fibrillin contain repeat motifs of?

Answer 37

Epidermal growth factor like modules

Question 38

How many EGF motifs does Fibrillin normally have?

Answer 38

47 EGF motifs, 43 of which bind Ca2+

Question 39

What syndrome is associated with cardiovascular and skeletal systems alongside fibrillin misfolding?

Answer 39

Marfan’s syndrome

Question 40

What is the main component of fibroid silk?

Answer 40

Glycine, then alanine

Question 41

What is the structure of fibroid?

Answer 41

Sheets, stabilised by hydrogen bonds | Side chains perpendicular to the structural plane

Question 42

What are properties of covalent structures?

Answer 42

Little elongation and provide high tensile strength

Question 43

What allows high flexibility in spidroin (spider silk)?

Answer 43

Relatively weak van der waals contacts between sheets