the present invention discloses a modified tumor necrosis factor - alpha converting enzyme catalytic domain , that unlike the native tace catalytic domain , is stable at high protein concentrations . the present invention further discloses methods for generating crystals of the modified tace protein in protein - ligand complexes with a number of inhibitors . in addition , the present invention discloses methods of using the proteins , crystals and / or three - dimensional structures obtained to identify compounds that can modulate the enzymatic activity of tace .