lecture 21 - fibrous proteins & alpha keratin

Question 1

explain the structure of fibrous proteins

Answer 1

• usually composed of one type of secondary structure that doesn’t fold up
• thus, secondary structure = tertiary structure
• which results in an extended shape

Question 2

fibrous proteins are usually composed of many hydrophobic residues, T or F? why?

Answer 2

• true

- allows for the formation of quaternary structure

Question 3

how does the tertiary structure of fibrous proteins form?

Answer 3

• multiple polypeptide chains pack together to form an ordered array (bc hydrophobic)
• this results in the formation of larger supramolecular structures

Question 4

are fibrous proteins rigid or flexible?

Answer 4

• can be either

- depends on function

Question 5

what are the primary functions of fibrous proteins?

Answer 5

• support (CT)
• provide force/shape (muscle)
• protection (skin/nails/horns)

Question 6

define alpha keratin

Answer 6

• family of proteins that are a component of hair, nails and horns
• differentiated to these areas by the sequence and structural features

Question 7

explain the primary structure of alpha keratin

Answer 7

• heptad repeat (a-b-c-d-e-f-g)n

- where ‘a’ and ‘d’ are typically hydrophobic

Question 8

explain the secondary structure of alpha keratin

Answer 8

slightly distorted alpha helix:
-normal = 3.6 res/turn and 5.4 A pitch
-keratin = 3.5 res/turn and 5.1 A pitch
(causes a slight turn in the helix)

Question 9

explain the tertiary structure of alpha keratin

Answer 9

single alpha helix

Question 10

explain the quaternary structure of alpha keratin

Answer 10

• 2 supertwisted alpha helices intertwined (each one wraps around the other)
• interface of Z helices formed by the ‘a’ and ‘d’ residues of the heptad repeat
• results in the potential to form salt bridges between ‘e’ and ‘g’
• residues ‘b’, ‘c’ and ‘f’ may be more polar and can interact favouably with the solvent

Question 11

are amino acid sequences different for each member of tha alpha keratin family? what does this mean?

Answer 11

• yes
• hair will have diff aa and structure than nails
• which affects function

Question 12

if we had an alpha-helical coiled coil with a pitch of 400A, ~88 helical turns and ~300 aa residues, what would be the result?

Answer 12

coiled coils associate to form supramolecular structures

Question 13

what is a key component to alpha keratin proteins?

Answer 13

their flexibility due to their structure

Question 14

what are the important features of alpha keratin for hair?

Answer 14

• contains cys residues
• allows u to get a perm which is where you reduce cys-cys bonds to cys-SH bonds resulting in curly hair
• can reoxidize cys to form disulphide bonds

Question 15

what are the important features of alpha keratin for nails?

Answer 15

it contains aa sequence features that enhance the rigidity of supramolecular structures