Hf. Zhang et al., STRUCTURAL AND PHYSICAL-PROPERTIES OF A NECROSIS-INDUCING TOXIN FROM PYRENOPHORA-TRITICI-REPENTIS, Phytopathology, 87(2), 1997, pp. 154-160
Cultivar-specific toxic metabolites of Pyrenophora tritici-repentis ar
e involved in the appearance of necrotic and chlorotic foliar lesions
characteristic of tan spot. A P. tritici-repentis necrosis-inducing to
xin, Ptr necrosis toxin, was purified from isolate 86-124, sequenced b
y gas-phase amino acid microsequencing, and characterized by circular
dichroism (CD) spectroscopy and isoelectric focusing. The purified pro
tein had a similar amino acid composition and molecular weight as prev
iously reported. Analysis of the CD spectrum from 178 to 250 nm indica
ted a protein consisting of 13% alpha-helix, 36% antiparallel beta-she
et, 25% turns, and 25% other structures. The Ptr necrosis toxin from i
solate 86-124 has an isoelectric point near pH 10. Using overlapping p
roteolytic fragments obtained from the toxin, a sequence of 101 contin
uous amino acids was obtained, but the amino terminus was blocked and
9 to 16 amino acids could not be sequenced. Secondary structure predic
tion based on the amino acid sequence indicated a beta-sheet protein w
ith little alpha-helix, which is in agreement with the structure deter
mined by CD spectroscopy. Sequence analysis indicated the presence of
a possible membrane adhesion site and several possible phosphorylation
sites that may be involved in phytotoxicity.