Selenium is an essential trace element in mammals, due to its presence in selenium-containing proteins (selenoproteins) in the form of selenocysteine (Sec). Sec is encoded by UGA codon and is known as the 21st amino acid in the genetic code. Mammals have 24-25 selenoproteins, which (with one exception) contain only one Sec residue. In proteins with known functions, Sec is used as a catalytic redox-active residue. Many selenoproteins evolved from thiol oxidoreductases, which replaced cysteine (Cys) with a catalytically superior Sec residue. However, the reasons Sec is used in catalysis are not fully clear, as most selenoproteins have related proteins that contain Cys in place of Sec. The use of Sec in proteins points to the location of the active site and can be used to identify catalytic Cys residues in related thiol oxidoreductases.

Biochemistry of selenium-containing proteins

244th National Meeting (2012)

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