Assume that this beta sheet is part of a beta barrel transme

Assume that this beta sheet is part of a beta barrel transmembrane domain. If the amino acid Indicated by the arrow is glutamine, which of the following is most likely to be the next amino add in the chain? Explain your answer. (gray= carbon; blue=nitrogen; red=oxygen, purple=hydrogen; R groups not shown) a. Lysine b. Proline c. Serine d. Valine

Solution

Beta barrels are formed from beta sheets, which are twisted and coiled. This forms a closed structure which acts like a pore and present in transmembrane region. Now the structure is observed as alternative polar and hydrophobic amino acids.

Now here if its glutamine [which is a polar amino acid], the next one has to be a hydrophobic amino acid. Option C is incorrect because Serine is also a polar amino acid. Option B is also incorrect because Proline due to its conformation, is present at the turns. Lysine is a positively charged amino acid, thus Option A is also incorrect. Thus we are left with Option D, which is a polar amino acid and fits the criteria- Valine.

Option D-Valine