Molecular cloning and characterization of rat ST1B1 and human ST1B2 cDNAs, encoding thyroid hormone sulfotransferases

Human and rat cDNAs encoding thyroid hormone sulfotransferases have been isolated from their liver cDNA libraries. The isolated sulfotransferases, termed rat ST1B1 and human ST1B2, share 77 and 74% homologies at nucleotide and deduced amino acid levels. These forms showed less than 36 and 56% homologies to hydroxysteroid and aryl sulfotransferases, indicating that they constitute a new gene subfamily of aryl sulfotransferase. Expression of ST1B1 and ST1B2 in COS-1 cells resulted in the appearance of 33.0 and 32.5 kDa proteins, respectively, whose mobilities were identical with proteins detected in rat and human livers in Western blots using antibodies raised against ST1B1 and ST1B2 produced in Escherichia coli. The recombinant forms catalyzed sulfation of p-nitrophenol, 3,3',5-triiodothyronine (T₃) and dopamine, but not of β-estradiol and dehydroepiandrosterone, ST1B1 and ST1B2 showed higher affinities for formation of T₃ sulfate (apparent K(m) 40.2 and 63.5 μM, respectively) than did thermostable phenol sulfotransferase ST1A3 (apparent K(m) 413 μM) or thermolabile phenol sulfotransferase ST1A5 (apparent K(m) 180 uM). These data indicate that the newly characterized sulfotransferases constitute a distinct ST1 subfamily of enzymes catalyzing the sulfation of T₃ as a typical endogenous substrate in rats and humans.