The present invention discloses purified polypeptides that comprise an active ADAM33 catalytic domain. In addition, the present invention discloses nucleic acids that encode the polypeptides of the present invention. The present invention also discloses methods of growing X-ray diffractable crystals of polypeptides comprising the active ADAM33 catalytic domain. In addition, the present invention discloses methods of using the X-ray diffractable crystals of ADAM33 in structure-based drug design to identify compounds that can modulate the enzymatic activity of ADAM33. The present invention also discloses methods of treating respiratory disorders by administering therapeutic amounts of the ADAM33 catalytic domain.