Mutation of the Secys residue 266 in human type 2 selenodeiodinase alters 75Se incorporation without affecting its biochemical properties.
Type 2 deiodinase (D2) is a low Km iodothyronine deiodinase that metabolizes thyroxine (T4) to the active metabolite T3. We have recently shown that the cDNA for the human D2 coding region contains two in-frame selenocysteine (TGA) codons. The 3' TGA is seven codons 5' to a universal stop codon, TAA. The human D2 enzyme, transiently expressed in HEK-293 cells, can be in vivo labeled with 75Se as a doublet of approximately 31 kDa. This doublet is consistent with the possibility that the carboxy-terminal TGA codon can either encode selenocysteine or function as a stop codon. To test this hypothesis we mutagenized the second selenocysteine codon to a cysteine (TGC) or to an unambiguous stop codon (TAA). While the selenium incorporation pattern is different between the wild-type and mutant proteins, the deiodination properties of the enzyme are not affected by mutating the 3'TGA codon. Thus, we conclude that neither this residue nor the remaining seven carboxy-terminal amino acids are critical for the deiodination process.
Salvatore
D
D
Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Harney
J W
JW
Larsen
P R
PR
D000818:Animals; D006801:Humans; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D051381:Rats; D017279:Selenocysteine / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D000097564:Iodothyronine Deiodinase Type II
D007453:Iodide Peroxidase; D017279:Selenocysteine; D000097564:Iodothyronine Deiodinase Type II