Inhibition of staphylococcal alpha-toxin by covalent modification of an arginine residue.

The effects of 1,2-cyclohexanedione and phenylglyoxal on staphylococcal alpha-toxin were studied. Modification of one arginine residue in alpha-toxin was sufficient to render the toxin nonhemolytic with no conformational change. Modified alpha-toxin did not protect cells from hemolysis by native alpha-toxin. An arginine residue is therefore at or near the binding site of alpha-toxin. Trypsin digestion of modified alpha-toxin generated a 20 kDa fragment which was isolated using a boric acid gel column. Upon regeneration, this 20 kDa fragment was not recognized by a population of antibodies which prevented alpha-toxin binding. The fragment was recognized by antibodies directed against post-binding events. However, the antibinding antibodies recognized the intact modified toxin. This leads us to conclude that antibinding determinants are not found directly in the binding site or are conformationally masked.