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Journal of Bacteriology, December 2007, p. 8719-8726, Vol. 189, No. 23
0021-9193/07/$08.00+0     doi:10.1128/JB.00741-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Structure and Biological Activities of Beta Toxin from Staphylococcus aureus{triangledown} ,{dagger}

Medora Huseby,1 Ke Shi,1 C. Kent Brown,1,{ddagger} Jeff Digre,1 Fikre Mengistu,1 Keun Seok Seo,3 Gregory A. Bohach,3 Patrick M. Schlievert,2 Douglas H. Ohlendorf,1 and Cathleen A. Earhart1*

Department of Biochemistry, Molecular Biology and Biophysics,1 Department of Microbiology, University of Minnesota, Minneapolis, Minnesota,2 Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, Idaho3

Received 10 May 2007/ Accepted 6 September 2007

Beta toxin is a neutral sphingomyelinase secreted by certain strains of Staphylococcus aureus. This virulence factor lyses erythrocytes in order to evade the host immune system as well as scavenge nutrients. The structure of beta toxin was determined at 2.4-Å resolution using crystals that were merohedrally twinned. This structure is similar to that of the sphingomyelinases of Listeria ivanovii and Bacillus cereus. Beta toxin belongs to the DNase I folding superfamily; in addition to sphingomyelinases, the proteins most structurally related to beta toxin include human endonuclease HAP1, Escherichia coli endonuclease III, bovine pancreatic DNase I, and the endonuclease domain of TRAS1 from Bombyx mori. Our biological assays demonstrated for the first time that beta toxin kills proliferating human lymphocytes. Structure-directed active site mutations show that biological activities, including hemolysis and lymphotoxicity, are due to the sphingomyelinase activity of the enzyme.

* Corresponding author. Mailing address: 6-155 Jackson Hall, 321 Church St. SE, Minneapolis, MN 55455. Phone: (612) 625-5118. Fax: (612) 624-5121. E-mail: Earhart{at}umn.edu

{triangledown} Published ahead of print on 14 September 2007.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Department of Biochemistry, Duke University, Durham NC.

Journal of Bacteriology, December 2007, p. 8719-8726, Vol. 189, No. 23
0021-9193/07/$08.00+0     doi:10.1128/JB.00741-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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