Question

Why would phenylalanine and aspartic acid be occasionally found together on a protein surface? What function would this site likely perform?

Answer 1

Phenylalanine being a non-polar, hydrophobic (water hating) amino acid preferred to be buried in the hydrophobic core of the protein. Almost all Proteins are found to be in the aqueous environment of cells. Hence the amino acids of primary structure of protein reacts with the water molecule and the hydrophobic amino acids of the proteins are buried inside the hydrophobic core of it, whereas the hydrophilic amino acid are found together at the protein surface.

Aspartic acid (negatively charged) being a polar, hydrophilic (water loving) amino acid can be usually found at the surface of the protein.