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SFP > Bonev - Structural proteins > Flashcards

Bonev - Structural proteins Flashcards

1
Q

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

A
  • Long, filamentous
  • Insoluble
  • Contain unusual amino acids
  • Often contain cross-linked polypeptide chains (polypeptides are covalently linked together to give a more stable structure)
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2
Q

What happens to keratin when epithelial cells die?

A

Keratin is retained within the cells and produced

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3
Q

Where is a-keratin predominantly found?

A

Outermost layer of skin, horns, hooves, and hair

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4
Q

Where are b-keratins found?

A

Feathers, scales

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5
Q

What type of structure does keratin form?

A

Forms alpha helical structures in a right-handed way

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6
Q

Which way does it supercoil though?

A

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

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7
Q

How many residues are present per turn in the protofilaments?

A

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

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8
Q

What is the pitch?

A

0.51nm

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9
Q

What is the pitch for the LH supercoiling?

A

21nm

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10
Q

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

A
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11
Q

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

A

Heptad helical wheel

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12
Q

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

A

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

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13
Q

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

A

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

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14
Q

Where is collagen found?

A

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

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15
Q

Which amino acid comprises 33% of collagen?

A

Glycine

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16
Q

Why is tryptophan not found in collagen?

A

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

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17
Q

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

A

1000 amino acids

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18
Q

What handedness are they each?

A

Right-handed

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19
Q

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

A
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20
Q

Why does collagen have proline present in its structure?

A

Because it is unable to form hydrogen bonds

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21
Q

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

A

Because a reduced amount of hydrogen bonding leads to increased flexibility

22
Q

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

A

Hydroxyproline

23
Q

How does hydroxyproline work?

A

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

24
Q

Helical pitch is around 0.95nm with 3.3 residues per turn

A
25
Q

Why is it important to have glycine in the structure?

A

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

26
Q

What is the difference between collagen and tropocollagen?

A

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

27
Q

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

A

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

28
Q

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

A
29
Q

An allysine and lysine can react together to form what?

A

Schiff base with no chemically active group

30
Q

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

A

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

31
Q

Why is glycosylation needed?

A

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

32
Q

Which amino acids make up collagen?

A

Glycine, proline, alanine, hydroxyproline, and others

33
Q

Where does a mutation tend to occur in collagen?

A

Glycine

34
Q

What does this lead to?

A

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

35
Q

Where is elastin found?

A

Connective tissue like arterial walls and ligaments

36
Q

What is it mainly composed of?

A

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

37
Q

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

A

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

38
Q

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

A

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

39
Q

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

A

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

40
Q

What does this lead to?

A

Extensive growth of organism, extended vasculature

41
Q

Where is fibroin secreted from?

A

Insects and arachnids

42
Q

What is the amino acid content?

A

Gly 45%, Ala 30%

43
Q

What is the main secondary structure found in fibroin?

A

Antiparallel beta sheets

44
Q

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.

A
45
Q

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

A

Crystalline domains

46
Q

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

A

A lot of strength and rigidity

47
Q

What holds this crystalline structure together?

A

Sericins

48
Q

Which enzyme converts lysine to allysine in collagen?

A

Lysyl oxidase

49
Q

What is the purpose of allysine being produced in collagen?

A

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

50
Q

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

A

Lysinonorleucine

51
Q

Why is this important in collagen?

A

Provides structural stability

SFP (14 decks)

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