Human liver thermostable phenol sulfotransferase its PST: CDNA cloning, bacterial expression and characterization

Sulfate conjugation is important in regulating the biologic activity of many compounds. Cytosolic TS PST catalyzes this reaction using such substrates as p-nitrophenol (pIMP) and triiodothyronine. To study TS PST in the absence of other potentially contaminating activities, we isolated and characterized a cDNA clone of an allelic variant of TS PST from a human liver cDNA library. To characterize this variant, the clone was expressed in transiently transfected COS-1 cells and as a fusion protein with the bacterial gene mal E. Both systems produced biologically active enzymes with V_max values for COS-1 expressed and fusion protein activities of 0.01 and 611.7 nmol/min/mg protein, respectively. Apparent K_m values for pNP were 0.67 μM and 0.25 νM, respectively; and apparent K.m values for 3'-phosphoadenosine 5' phosphosulfate were0.29/yM and O.tSfjM, respectively. The addition of the mal E coding region at the amino terminus of TS PST altered the enzyme activity by rendering it less thermostable, more sensitive to the inhibitor 2,6-dichloro-4-nitrophenol (DCNP) and more resistant to inhibition by NaCI. Conclusions: This TS PST allelic variant was similar to known TS PST variants. Definitive characterization of a fusion orotein is reauired to determine its similarity to the native protein.