Orphan selenoproteins

Selenoproteins contain selenium in stoichiometric amounts. Most are synthes ized by a process that decodes UGA codons as selenocysteine. Twelve animal selenoproteins have been characterized, and biochemical functions have been described for all but three. Two of these "orphan" selenoproteins are disc ussed in this paper. Selenoprotein P is an extracellular glycoprotein that contains multiple selenocysteines. It binds heparin and associates with end othelial cells. Two isoforms have been identified. Plasma concentration of selenoprotein P correlates with protection against diquat liver injury, sug gesting that the protein protects against oxidant injury. Selenoprotein W i s a small intracellular protein that contains one selenocysteine. It binds glutathione and has been suggested to function in oxidant defense, The post ulated oxidant defense properties of these selenoproteins are consistent wi th the facile thiol-redox properties of selenocysteine. It can be predicted that more proteins will be discovered that take advantage of the chemical properties of selenium. BioEssays 21:231-237, 1999. (C) 1999 John Wiley & S ons, Inc.