Abstract
Tyrosine O-sulfation is a common posttranslational modification of proteins in all multicellular organisms. This reaction is mediated by a Golgi enzyme activity called tyrosylprotein sulfotransferase (TPST) that catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to tyrosine residues within acidic motifs of polypeptides. Tyrosine O-sulfation has been shown to be important in protein-protein interactions in several systems. For example, sulfation of tyrosine residues in the leukocyte adhesion molecule P-selectin glycoprotein ligand 1 (PSGL-1) is required for binding to P-selectin on activated endothelium. In this report we describe the purification of TPST from rat liver microsomes based on its affinity for the N-terminal 15 amino acids of PSGL-1. We have isolated human and mouse TPST cDNAs that predict type II transmembrane proteins of 370 amino acid residues with almost identical primary structure. The human cDNA encodes a fully functional N-glycosylated enzyme with an apparent molecular mass of approximately 54 kDa when expressed in mammalian cells. This enzyme defines a new class of Golgi sulfotransferases that may catalyze tyrosine O-sulfation of PSGL-1 and other protein substrates involved in diverse physiologic functions including inflammation and hemostasis.