The present invention discloses purified polypeptides that comprise an active human 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 human ADAM33 catalytic domain. The present invention further discloses a crystalline form of a catalytic domain of human ADAM33. In addition, the present invention discloses methods of using the X-ray diffractable crystals of human ADAM33 in structure based drug design to identify compounds that can modulate the enzymatic activity of human ADAM33. The present invention also discloses methods of treating respiratory disorders by administering therapeutic amounts of the human ADAMS33 catalytic domain.