Protein-Protein Interaction between the Murine Toxin of Pasteurella pestis and Bovine Heart Mitochondrial Structural Protein

The solubility of the homogeneous, nonenzymatic structural protein isolated and purified from bovine heart mitochondria when incubated with the murine toxin of Pasteurella pestis at pH 11.0 increases as the concentration of the toxin is increased. This indicates that a protein-protein interaction occurs between the monomeric units of the structural protein and the toxin. This interaction results in the decline of the toxicity of the toxin. The extent to which the toxicity is diminished depends upon the ratio of structural protein to toxin in the incubation mixture. Double diffusion gel precipitation reactions with plague murine toxin incubated with structural protein revealed that the decrease in the toxicity of the toxin is correlated with the disappearance of the bands exhibited by both toxin A and toxin B, the two protein species comprising plague murine toxin. No interaction is observed between the toxin and polymeric structural protein. There is, however, an indication of a slight decrease in the toxicity of the toxin. Under the latter conditions, the band for toxin A is not visible in double diffusion gel precipitation reactions whereas the band for toxin B remains intact. Bovine serum albumin does not interact with plague murine toxin nor does it affect its toxicity. These results suggest that the interaction between plague murine toxin and monomeric structural protein involves binding of the two proteins. The relationship that this protein-protein interaction may have to the known inhibitory effect of the toxin on the electron transport system is discussed.