An effective method for profiling the selenium-binding proteins using its reactive metabolic intermediate.

Currently, the intracellular reduction and/or transport of selenium still remain unknown. Certain reduced forms of selenium species are thought to be reactive with various endogenous molecules, particularly thiol-containing proteins. In this study, a profiling method for identifying the selenium-binding proteins using L-penicillamine selenotrisulfide (PenSSeSPen) as a model of the selenium metabolic intermediate was applied to the cell lysate generated from the rat liver. Several proteins with cysteine thiol were found to be reactive with PenSSeSPen through the thiol-exchange reaction by MALDI TOF-MS analysis. The most distinctive cysteine-containing protein at m/z 14,313 in the liver cell lysate was identified as the liver fatty acid-binding protein based on a rat protein database search and a tryptic fragmentation experiment. This methodology could be used for determining the selenium-binding proteins and/or selenium-interactive species and provide a better understanding of the selenium metabolism and utilization in biological systems.