Residue-Specific Chemical Modification of Proteins

Abstract

Over the past 50 years a variety of reagents have been found that covalently modify specific amino acid residues within proteins. Such compounds can be useful analytical tools for assessing the distribution of a particular amino acid type between the interior and surface of a folded protein molecule. The rationale for this type of analysis goes as follows. If there exist buried and surface exposed populations of a certain amino acid type within a protein, then treatment with a covalent modifying reagent under native conditions will only result in modification of the surface exposed residues. Those residues within the hydrophobic interior of the protein will not make contact with the modifying reagent, and will thus be protected from covalent modification. Comparison of the number of modification events per molecule of protein in the folded and unfolded (denatured) states can thus be used to describe the distribution of that amino acid type within the protein. This type of information is important in mapping out the surface topography of native proteins, and for assessing changes in surface exposure under different solution conditions, after effecting a conformational transition of a protein, or during stability studies.