EXISTENCE OF DISTINCT TYROSYLPROTEIN SULFOTRANSFERASE GENES - MOLECULAR CHARACTERIZATION OF TYROSYLPROTEIN SULFOTRANSFERASE-2

Tyrosylprotein sulfotransferase (TPST) is a 54- to 50-kDa integral mem brane glycoprotein of the trans-Golgi network found in essentially all tissues investigated, catalyzing the tyrosine O-sulfation of soluble and membrane proteins passing through this compartment. Here we descri be (i) an approach to identify the TPST protein, referred to as MSC (m odification after substrate crosslinking) labeling, which is based on the crosslinking of a substrate peptide to TPST followed by intramolec ular [S-35]sulfate transfer from the cosubstrate 3'-phosphoadenosine 5 '-phosphosulfate (PAPS); and (ii) the molecular characterization of a human TPST, referred to as TPST-2, whose sequence is distinct from tha t reported [TPST-1; Ouyang, Y.-B., Lane, W. S. & Moore, K, L, (1998) P roc, Natl. Acad, Sci. USA 95, 2896-2901] while this study was in progr ess, Human TPST-2 is a type II transmembrane protein of 377 aa residue s that is encoded by a ubiquitously expressed 1.9-kb mRNA originating from seven exons of a gene located on chromosome 22 (22q12.1), A 304-r esidue segment in the luminal domain of TPST-2 shows 75% amino acid id entity to the corresponding segment of TPST-1, including conservation of the residues implicated in the binding: of PAPS, Expression of the TPST-2 cDNA in CHO cells resulted in an approximate to 13-fold increas e in both TPST protein, as determined by MSC labeling, and TPST activi ty. A predicted 359-residue type II transmembrane protein in Caenorhab ditis elegans with 45% amino acid identity to TPST-2 in a 257-residue segment of the luminal domain points to the evolutionary conservation of the TPST protein family.