A Comprehensive Analysis of Selenium-Binding Proteins in the Brain Using Its Reactive Metabolite.
ABSTRACT
The intracellular metabolism of selenium in the brain currently remains
unknown, although the antioxidant activity of this element is widely
acknowledged to be important in maintaining brain functions. In this
study, a comprehensive method for identifying the selenium-binding
proteins using PenSSeSPen as a model of the selenium metabolite,
selenotrisulfide (RSSeSR, STS), was applied to a complex cell lysate
generated from the rat brain. Most of the selenium from L-penicillamine
selenotrisulfide (PenSSeSPen) was captured by the cytosolic protein
thiols in the form of STS through the thiol-exchange reaction
(R-SH+PenSSeSPen→R-SSeSPen+PenSH). The cytosolic protein species, which
reacted with the PenSSeSPen mainly had a molecular mass of less than
20 kDa. A thiol-containing protein at m/z 15155 in the brain cell lysate
was identified as the cystatin-12 precursor (CST12) from a rat protein
database search and a tryptic fragmentation experiment. CST12 belongs to
the cysteine proteinase inhibitors of the cystatin superfamily that are
of interest in mechanisms regulating the protein turnover and
polypeptide production in the central nervous system and other tissues.
Consequently, CST12 is suggested to be one of the cytosolic proteins
responsible for the selenium metabolism in the brain.