Keratin is a coiledcoil protein Answer the following questio

Keratin is a “coiled-coil” protein. Answer the following questions about keratin.

a)Keratin proteins have a “pseudorepeat” of how many residues?

b)At what positions are hydrophobic residues found in the pseudorepeat?

c)Why are there hydrophobic residues at those positions?

d)Polar residues are usually found at the remaining positions. Why? e)Which of the following possible peptides is most likely to be a pseudorepeat? (pick only one)

1. D-Q-I-E-V-E-R

2. W-Q-E-Y-E-R-D

3. I-Q-E-V-E-R-D

f)What is wrong, or less good, about the other two possibilities?

Solution

a) keratin protein has 7 resedues in the pseudorepeat

b) the first and fourth residue are hydrophobic

c) keratin is a coiled coil protein with 4 alpha helical coils and this pseudorepeat sequences are placed in the centre to hold the coils intact. It is mainly the hydrophobic interaction within these residues that maintain the structural integrity.

d polar residues can pocket themselves in the flanking region when there is a hydrophobic interaction between the hydrophobic aminoacids.

e I-Q-E-V-E-R-D

is most likely a pseudorepeat as it has polar residue in the first and fourth position and hydrophillic residues in the remaining positions

option 1 cannot be a pseudorepeat as it has a hydrophillic aminoacid in the first position and similarly option 2 has a non polar residue in position 4