Background: In animals, the 21st amino acid selenocysteine is incorporated into a
restricted subset of proteins by recoding of a UGA stop codon. This recoding requires a distinctive
selenocysteine insertion sequence in selenoprotein encoding mRNAs, trans-acting factors and in
most cases, adequate dietary intake of selenium. With one exception, selenoproteins contain a
single selenocysteine, which is incorporated with low translational efficiency. The exception is
selenoprotein P, which in some species is predicted to contain as many as 132 selenocysteines and
which is considered to play roles in selenium transport and storage.
Objective: This study aimed to develop comparative physiological and evolutionary perspectives
on the function(s) of selenoprotein P.
Methods: The review of the literature on the roles of selenoprotein P in diverse animals.
Results: Selenoprotein P contains multiple selenocysteines, making it energetically costly to
produce. Furthermore, it is often associated with detrimental effects to the animals that produce it.
Possible benefits that outweigh these costs include the general storage and transport of selenium;
the transport of both toxic and useful metal ions; and specific functions in reproduction and in the
Conclusion: A probable reconciliation of the negative effects of producing Selenoprotein P is its
benefit in terms of promoting reproductive success.