Differential Enzymatic Characteristics and Tissue-Specific Expression of Human TPST-1 and TPST-2

Abstract

Protein tyrosine sulfation is emerging as a widespread post-translational modification in multicellular eukaryotes. The responsible enzyme, named tyrosylprotein sulfotransferase (TPST), catalyzes the sulfate transfer from 3′-phosphoadenosine 5′-phosphosulfate to tyrosine residues of proteins. Two distinct TPSTs, designated TPST-1 and TPST-2, had previously been identified. In the present study, we cloned human TPST-1 and TPST-2 expressed and characterized the recombinant enzymes using peptide substrates. These enzymes displayed distinct acidic pH optima and stimulatory effects of Mn²⁺. Additionally, the activity of TPST-2, but not TPST-1, was stimulated in the presence of Mg²⁺. Compared with TPST-2, TPST-1 displayed considerably lower K_m and V_max for the majority of the tested peptide substrates, implying their differential substrate specificity. Quantitative real-time PCR analysis showed that although the two TPSTs were co-expressed in all 20 human tissues examined, the levels of expression of TPST-1 and TPST-2 varied significantly among different tissues. These latter findings may imply distinct physiological functions of TPST-1 and TPST-2.