Nuclease-sensitive binding of an Actinobacillus actinomycetemcomitans leukotoxin to the bacterial cell surface

A leukotoxin of Actinobacillus actinomycetemcomitans 301-b was solubilized from cell-associated membrane vesicles by treatment with externally added DNase and RNase and was further purified by a procedure which included ammonium sulfate fractionation, gel filtration chromatography, and ion-exchange chromatography. The purified toxin had a molecular mass of 113,000 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a high isoelectric point (approximately 8.8). From these characteristics, it was to be expected that the membrane vesicle toxin was almost identical to the leukotoxin extracted with polymyxin B in an earlier study (C.-C. Tsai, B. J. Shenker, J. M. DiRienzo, D. Malamud, and N. S. Taichman, Infect, Immun. 43:700-705, 1984). The treatment with DNase and RNase was also highly effective for solubilizing the leukotoxin directly from whole cells, suggesting that the toxin is secreted extracellularly but retained in nucleic acids on the outermost surface of bacterial cells.