Chemical Cleavage of Proteins at Aspartyl Residues

Abstract

One of the most commonly used methods for proteolysis uses cyanogen bromide to cleave the bond to the C-terminal side of methionyl residues. The reaction is highly specific with few side reactions and a typical yield of 90–100%. It is also relatively simple and adaptable to large or small scale. Since methionine is one of the least abundant amino acids, cleavage at that residue tends to generate relatively few peptides of size up to 10,000–20,000 Dalton. Such cleavage may be useful to confirm estimates of methionine content by amino acid analysis, which has a tendency to be somewhat inaccurate for this residue (1). Cyanogen bromide may be used for the purposes of peptide mapping and preparation of peptides for amino acid sequencing. In addition the method has been used to map the binding sites of antibodies (2) or ligands (3), whereas in combination with molecular engineering techniques, it has been used to cleave at specific points in order to generate functionally distinct domains (from hirudin, by Wallace et al. [4]) or proteins of interest from fusion proteins (5).