Proteins containing multiple, different unnatural amino acids and methods of making and using such proteins

A protein expressed in a mammalian cell, wherein the protein comprises two distinct unnatural amino acids incorporated into the protein at two site-specific locations, wherein the first unnatural amino acid (UAA) is a tryptophan analog selected from 5-HTP and 5-AzW and the second UAA is a leucine analog selected from LCA and Cys-5-N3.