Steroid Sulfatase Isozyme S (STS)

STS catalyzes the conversion of sulfated steroid precursors to estrogens during pregnancy. The encoded protein is found in the endoplasmic reticulum, where it acts as a homodimer.

The deduced 583-residue protein has a molecular mass of 63 kD and contains a 21- or 23-residue signal peptide, 4 possible N-linked glycosylation sites, and 2 potential membrane-spanning domains. Expression in hamster kidney cells (BHK-21) showed localization predominantly in the endoplasmic reticulum, with smaller fractions found in the Golgi, at the cell surface, and in endosomes and lysosomes. The major transcription start site was at position -221 with respect to the AUG translation initiation codon, and the amino acids were renumbered to make the initiating methionine +1.