Mapping Protein Disulfide Bonds by Mass Spectrometry.

Disulfide bonds are typically identified from protein tertiary and quaternary structures. By analyzing electron density maps of proteins, investigators can identify disulfide bonds based on the distance and the geometry between sulfur atoms of cysteine residues. However, there are many instances where the disulfide pairing in protein crystal structures differs from the pairing in the soluble protein. In this chapter, we describe how mass spectrometry can be used to identify new or unexpected disulfide bonds in proteins. The method is exemplified by identification of an unexpected disulfide bond linking Cys2528 and Cys2533 in von Willebrand factor. This same approach can apply to any protein.