STRUCTURE DETERMINATION OF TOLAASIN, AN EXTRACELLULAR LIPODEPSIPEPTIDE PRODUCED BY THE MUSHROOM PATHOGEN PSEUDOMONAS-TOLAASII PAINE

The principal active component of tolaasin, the Pseudomonas tolaasii toxin, which is responsible for brown blotch disease of mushrooms, is shown to be a lipodepsipeptide of M(r) 1985. The structure determined is beta-hydroxyoctanoyl-DELTA-But-D-Pro-D-Ser-D-Leu-D-Val-D-Ser-D-Leu-D-Val-L-Val-D-Gln-L-Leu-D-Val-DELTA-But-D-allo-Thr-L-Ile-L-Hse-D-Dab-L-Lys (cyclized via lactone formation between D-allo-Thr and the C-terminus) by a combination of fast atom bombardment mass spectrometry (FABMS), H-1 NMR, automated sequencing, and chiral gas chromatography. A minor component of the toxin (M(r) 1941) has a related structure in which the homoserine residue is substituted by glycine. In addition, the sequence of a modified form of the toxin, produced by a genetically engineered strain of P. tolaasii, is characterized.