Structural Origins of l(+)-Tartrate Inhibition of Human Prostatic Acid Phosphatase

Abstract

Acid phosphatase activity in the blood serum is usually separated into tartrate-resistant and tartrate-refractory, which is reported as the prostatic acid phosphatase level. Human prostatic acid phosphatase crystals soaked in N-propyl-L-tartramate were used to collect x-ray diffraction data to 2.9 A resolution under cryogenic conditions. Positive difference electron density, corresponding to the inhibitor, was found. The quality of the electron density maps clearly shows the orientation of the carboxylate and N-propyl-substituted amide groups. The hydroxyl group attached to C3 forms two crucial hydrogen bonds with Arg-79 and His-257. Previous crystallographic studies compiled on the tartrate-rat prostatic acid phosphatase binary complex (Lindqvist, Y., Schneider, G., and Vihko, P. (1993) J. Biol. Chem. 268, 20744-20746) erroneously positioned D-tartrate into the active site. Modeling studies have shown that the C3 hydroxyl group on the D(-)-stereoisomer of tartrate, which does not significantly inhibit prostatic acid phosphatase, does not form strong hydrogen bonds with Arg-79 or His-257. The structure of human prostatic acid phosphatase, noncovalently bound in N-propyl-L-tartramate, is used to develop inhibitors with higher specificity and potency than L(+)-tartrate.