A NEW MODE OF PORE ASSEMBLY BASED ON THE STRUCTURE OF INTERMEDILYSIN, A TOXIN SPECIFIC FOR HUMAN CELLS

Galina Polekhina,^a Rodney K. Tweten,^b and Michael W. Parker^a

^aSt. Vincent’s Institute of Medical Research, 9 Princes Street, Fitzroy, VIC 3065, Australia; ^bDepartment of Microbiology and Immunology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA

(galinap@medstv.unimelb.edu.au)

The pore-forming cholesterol-dependent toxins have been identified in numerous species from five different genera of Gram-positive bacteria, including Clostridium, Bacillus, Streptococcus, Listeria and Arcanobacterium [1]. Their toxicity arises from the transition of a monomeric water-soluble form to large self-associated pores in the membrane of target cells. Intermedilysin (ILY), a toxin produced by Streptococcus intermedius, is of particular interest due to its exclusive specificity for human cells in contrast to other related toxins and its role in deep-seated abscess formations in brain and liver [2]. Brain abscesses may give rise to meningitis. It has also been shown that ILY interacts with the protein receptor on the target cells [3] unlike other toxins that only require the presence of cholesterol in the target membrane.

We report the crystal structure of ILY that has been determined by combination of single isomorphous replacement and multiple anomalous dispersion techniques and has been refined to 2.3 Å. The structure reveals a profound bend to the rod-shaped molecule compared to the structure of the related toxin from Clostridium perfringens, perfringolysin O (PFO). Based on the structure of ILY and the reported fluorescent studies performed on PFO [3] we propose a new mode of pore assembly. We will offer an explanation as to why certain ions are required for stability of ILY and discuss the receptor specificity based on comparison of the structures of ILY and PFO.

References

1 Tweten, R. K., Parker, M. W. and Johnson, A. E. (2002) Curr. Top. Microbiol. Immunol. 257, 15-33.

2 Nagamune, H., Ohnishi, C., Katsuura, A., Fushitani, K., Whiley, R. A., Tsuji, A. and Matsuda, Y. (1996) Infection and Immunity 64, 3093-3100.

3 Ramachandran, R., Heuck, A. P., Tweten, R. K. and Johnson, A. E. (2002) Nat. Struct. Biol. 9, 823-827.