The role of disulfide bonds in structure and activity of chlorotoxin

Background: Chlorotoxin is a small scorpion peptide that inhibits glioma cell migration. We investigated the importance of a major component of chlorotoxin's chemical structure-four disulfide bonds-to its tertiary structure and biological function. Results: Five disulfide bond analogs of chlorotoxin were synthesized, with l-a-aminobutyric acid residues replacing each or all of the disulfide bonds. Chemical oxidation and circular dichroism experiments revealed that Cys III-VII and Cys V-VIII were essential for native structure formation. Cys I-IV and Cys II-VI were important for stability of enzymatic proteolysis but not for the inhibition of human umbilical vein endothelial cell migration. Conclusion: The disulfide bonds of chlorotoxin are important for its structure and stability and have a minor role in its activity against cell migration.