A method for probing the topography and interactions of proteins: Footprinting of myoglobin

We describe a procedure for mapping residues on the surface of a protein molecule to its sequence, using a scheme that is analogous to nucleic acid footprinting. The protein is end labeled radioactively and subjected to limited proteolysis, and the products are analyzed by denaturing polyacrylamide gel electrophoresis and autoradiography. The method is tested with the heme protein myoglobin and applied to mapping the (unknown) surface of the molecule lacking the heme group: apomyoglobin. Sites of protein- protein interaction can be identified, as illustrated by footprinting the association between myoglobin and an anti-myoglobin monoclonal antibody.