In most cases, mutations in the core of a protein that replace a smaller nonpolar side chain in the wild-type (e.g., Ala, Val) with a larger nonpolar side chain (e.g., Leu, Ile, Phe, Trp) in the mutant, result in significant destabilization and misfolding of the mutant. What feature of the protein core explains this observation? Why would such a mutation prevent a protein from folding properly?