1.D.4 The Tolaasin Channel-forming (Tolaasin) Family

Tolaasin is a lipodepsipeptide toxin produced by the mushroom pathogen, Pseudomonas tolaasii. The toxin is hemolytic, and hemolysis occurs optimally at pH 6.5 with rates that increase with temperature and decrease with increasing concentrations of divalent metal ions. Tolaasin is active against mushrooms and other fungi, causing brown blotch disease in cultivated mushrooms. It is also active against plant and animal cells and Gram-positive bacteria, but not Gram-negative bacteria (Rainey et al., 1991). Gram-negative bacteria are sensitive to tolaasin in the presence of polymyxin B, but P. tolaasii is not sensitive even in the presence of polymyxin B.

Tolaasin partitions into artificial and biological membranes forming voltage-gated, cation-selective ion channels. Two types of ion conducting channels in lipid bilayers are formed by tolaasin, suggesting that it can form at least two different oligomeric complexes (Cho and Kim, 2003).

The generalized transport reaction is:

Cation (in) Cation (out)



Bender, C.L., F. Alarcòn-Chaidez, and D.C. Gross. (1999). Pseudomonas syringae phytotoxins: mode of action, regulation, and biosynthesis by peptide and polyketide synthetases. Microbiol. Mol. Biol. Rev. 63: 266-292.

Cho, K.-H. and Y.-K. Kim. (2003). Two types of ion channel formation of tolaasin, a Pseudomonas peptide toxin. FEMS Microbiol. Lett. 221: 221-226.

Rainey, P.B., C.L. Brodey, and K. Johnstone. (1991). Biological properties and spectrum of activity of tolaasin, a lipodepsipeptide toxin produced by the mushroom pathogen Pseudomonas tolaasii. Physiol. Mol. Plant Pathol. 39: 57-70.


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