Chemical Cleavage of Proteins at Cysteinyl Residues
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Cysteine is a significant amino acid residue in that it can form a disulfide bridge with another cysteine (to form cystine). Such disulfide bridges are important determinants of protein structure. No known endoproteinase shows specificity solely for cysteinyl or cystinyl residues, although endoproteinase Asp-N is able to hydrolyze bonds to the N-terminal side of aspartyl or cysteinyl residues. Modification of the former (1) can generate specificity for cysteinyl residues. Again, as discussed by Aitken (2), modification of cysteinyl to 2-aminoethylcysteinyl residues makes the bond to the C-terminal side susceptible to cleavage by trypsin or the bond to the N-terminal side sensitive to Lys-N. However, specific cleavage of bonds to the N-terminal side of cysteinyl residues may be achieved in good yield by chemical means (3). The cleavage generates a peptide blocked at its N-terminus as the cysteinyl residue is converted to an iminothiazolidinyl residue, but peptide sequencing can be carried out after conversion of this residue to an alanyl residue (4).
KeywordsDisulfide Bridge Specific Cleavage Raney Nickel Frequent Amino Acid Modification Buffer
- 1.Wilson, K. J., Fischer, S., and Yuau, P. M. (1989) Specific enzymatic cleavage at cystine/cysteine residues. The use of Asp-N endoproteinase, in Methods in Protein Sequence Analysis (Wittman-Liebold, B., ed.), Springer-Verlag, Berlin, pp. 310–314.Google Scholar