Final answer:
Leucine is the correct amino acid residue among the choices given to provide a side chain that is capable of increasing the hydrophobicity of a binding site due to its nonpolar and hydrophobic aliphatic side chain.
Step-by-step explanation:
The question asks which of the following amino acid residues would provide a side chain capable of increasing the hydrophobicity of a binding site: 1) Alanine 2) Aspartic acid 3) Glutamic acid 4) Leucine. Hydrophobic amino acids are generally nonpolar and do not interact well with water. Among the options provided, Alanine and Leucine are both nonpolar amino acids. Leucine, being bulkier than alanine, has a larger hydrophobic aliphatic side chain, which would contribute more significantly to the hydrophobicity of the binding site. Therefore, the correct answer is Leucine, which is known for its ability to participate in hydrophobic interactions within proteins.