Question

where would you expect to find the amino acid leucine in a protein structure?
forming the more flexible parts of the protein to confer elasticity
on the surface of a protein, interacting with water
interacting with other amino acids in the interior of a protein
in the nonrepetitive regions that flank core repeated sequences

Explanation:

Leucine is a hydrophobic (water-repelling) amino acid. In protein folding, hydrophobic amino acids tend to cluster in the interior of the protein to avoid contact with the aqueous environment, interacting with other hydrophobic amino acids there.

Answer:

interacting with other amino acids in the interior of a protein