Question

If the following section of a polypeptide is folded into an alpha-helix at pH 7, the carbonyl group of the glutamate residue will interact via backbone hydrogen bonding with which other residue?

Glu-Ser-Val-Asp-Gly-Leu-Ala
A. Leucine
B. Valine
C. Aspartic acid
D. Glycine
E. Alanine

Answer 1

In an alpha-helix, hydrogen bonds form between every fourth amino acid residue, so the carbonyl group of glutamate (Glu) will hydrogen bond with leucine (Leu) in the given polypeptide sequence.

Step-by-step explanation:

If the polypeptide section Glu-Ser-Val-Asp-Gly-Leu-Ala is folded into an alpha-helix at pH 7, we know that in an alpha-helix each turn is stabilized by hydrogen bonds between the backbone carbonyl oxygen atom and the amide hydrogen atom four residues earlier. Considering that each helical turn of the alpha helix comprises 3.6 amino acid residues, the glutamate residue's carbonyl group would form a hydrogen bond with the residue four positions down the sequence, which in this case is leucine. Therefore, the correct answer to the question - the carbonyl group of the glutamate residue will interact via backbone hydrogen bonding with which other residue - is A. Leucine.