Hello and i need help with this question

When an integral membrane protein folds, which of the following pairs of
amino acid residues would you expect to find on the exterior of the
folded protein?

A. aspartate and glutamate
B. aspartate and serine
C. aspartate and valine
D. isoleucine and valine
E. serine and valine

The correct answer is D but can someone explain my why D. Both isoleucine and valine are hydrophobic and i thought they would be inside of the protein ?
many thanks

Reply 1

Syed100

You are correct that isoleucine and valine are hydrophobic, and they would normally be found inside of a protein. However, integral membrane proteins are embedded in the cell membrane, which is a hydrophobic environment. In order to interact with the cell membrane, integral membrane proteins have to have some hydrophobic amino acids on their exterior. Isoleucine and valine are two of the most hydrophobic amino acids, so they are often found on the exterior of integral membrane proteins.

The other answer choices are not correct because they contain at least one hydrophilic amino acid. Aspartic acid and glutamate are both acidic, and serine is a polar amino acid. These amino acids would not be able to interact with the hydrophobic cell membrane.

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