Crystal growth of human estrogenic 17β-hydroxysteroid dehydrogenase

Estrogenic 17β-hydroxysteroid dehydrogenase from human placenta, an enzyme of low solubility, has been crystallized in the complex form with its cofactor NADP⁺. These are the first crystals with X-ray diffraction quality for structure analysis from any human steroid-converting enzyme. The crystals were grown by vapor diffusion in the presence of 0.06% β-octylglucoside, using polyethylene glycol 4000 as the precipitant (27–28%) and one of several different salts at pH 7.5 and room temperature. Crystals grown with magnesium chloride diffract up to 2.4 Å. The most important steps leading to the rapid success of the crystallization of this labile enzyme were the following: preparation of a highly active and homogeneous enzyme protein using a rapid procedure; the choice of a suitable enzyme buffer system and a detergent favorable to maintaining high activity and solubility for the enzyme; and a combined screening procedure. The present study could be useful for the successful crystal growth of other hydrophobic or membrane-bound proteins.