Estrone sulfatase: Probing structural requirements for substrate and inhibitor recognition

The enzyme-catalyzed desulfation of steroids is a transformation that plays an important role in steroid biosynthesis. Conversion of steroid sulfates to unconjugated steroids may provide a source of steroids for processes such as steroid transport and the growth and proliferation of breast cancer. Steroid sulfatase catalyzes the hydrolysis of 3 beta-hydroxysteroid sulfates. To identify structural features important in enzyme-inhibitor interaction, a variety of steroidal and non-steroidal phosphate esters were synthesized and tested as inhibitors of steroid sulfatase activity. We report that the basic structure for enzyme-inhibitor binding does not include the steroid nucleus. Furthermore, the hydrophobicity of the nonsteroidal phosphates was determined to be an important factor for optimal inhibition. The monoanionic form of the phosphorylated compounds was found to be the inhibitory species. The best non-steroidal inhibitor of steroid sulfatase activity was n-lauroyl tryamine phosphate with a K-i of 3.6 mu M and 520 nM at pH 7.5 and 7.0. The poorest non-steroidal based inhibitor of sulfatase activity was tetrahydronaphthyl phosphate with a K-i of 870 and 360 mu M at pH 7.5 and 7.0.