Ricin peptide mapping

The identification of reactive or chemically modified residues of proteins is often extremely important for the characterization of proteins and their activity. Peptide mapping in conjunction with Edman sequencing and/or mass spectrophotometric analysis has been the method of choice to accomplish this characterization. However, this approach alone may not be sufficient or optimal for every situation as was the case when trying to identify the affinity ligand attachment sites on the B-chain of blocked ricin (Lambert et al., 1991a). 

Identification of the residues of ricin involved in the covalent linkage to the affinity ligand is important for complete characterization of the cytotoxic effector moiety and to ensure consistency of the immunoconjugate product. However, due to the intrinsic heterogeneity of the ligand, isolation of individual species of ligand-bound B-chain peptides by traditional peptide mapping has not been possible. 

C. Peptide mapping of the Ricin B-chain attachment sites... 

Here we report the results obtained using MIANS-labeling in conjunction with affinity chromatography to map free thiols in reduced, native ricin A-chain. We further describe the results obtained when utilizing this method to isolate ligand-bound ricin B-chain peptides. 

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