Question

Hydrophobic residues usually appear at the first and fourth positions in the seven-residue repeats of polypeptides that form coiled coils. The first and fourth side chains are buried in the coiled coil, but the remaining side chains are exposed to the solvent and therefore tend to be polar or charged. Which of the following sequences is more likely to appear in a coiled coil? 275 0.728 a) Ile-Gln-Glu-Val-Glu-Arg-Asp## 15 0.040 b) Trp-Gln-Glu-Tyr-Glu-Arg-Asp 11 0.029 c) Ile-Gln-Glu-Val-Glu-Ala-Asp 8 0.021 d) Trp-Gln-Glu-Tyr-Glu-Ala-Asp

Answer 1

Correct option is (a) Ile–Gln–Glu–Val–Glu–Arg–Asp as according to question,the first and fourth side chains of the two helices of a coiled coil form buried hydrophobic interacting surfaces, but the remaining side chains are exposed to the solvent and therefore tend to be polar or charged.although the residues at positions 1 and 4 in both sequences are hydrophobic, Trp and Tyr aremuch larger than Ile and Val and would therefore not fit as well in the area of contact between the two polypeptides in a coiled coil