Structural and physical properties of a necrosis-inducing toxin from Pyrenophora tritici-repentis

• Published in: Phytopathology Vol. 87; no. 2; pp. 154 - 160
• Main Authors: ZHANG, H.-F, FRANCL, L. J, JORDAHL, J. G, MEINHARDT, S. W
• Format: Journal Article
• Language: English
• Published: St. Paul, MN American Phytopathological Society 01.02.1997
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; Phytopathology. Animal pests. Plant and forest protection; Monocotyledones; Purification; Plant pathogen; Phytotoxin; Molecular structure; Secondary structure; Cereal crop; Fungi; Toxin; Structure activity relation; Gramineae; Angiospermae; Pyrenophora tritici-repentis; Ascomycetes; Spermatophyta; Aminoacid sequence; Triticum aestivum; Thallophyta
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO.1997.87.2.154

ABSTRACT Cultivar-specific toxic metabolites of Pyrenophora tritici-repentis are involved in the appearance of necrotic and chlorotic foliar lesions characteristic of tan spot. A P. tritici-repentis necrosis-inducing toxin, Ptr necrosis toxin, was purified from isolate 86-124, sequenced by gas-phase amino acid microsequencing, and characterized by circular dichroism (CD) spectroscopy and isoelectric focusing. The purified protein had a similar amino acid composition and molecular weight as previously reported. Analysis of the CD spectrum from 178 to 250 nm indicated a protein consisting of 13% alpha-helix, 36% antiparallel beta-sheet, 25% turns, and 25% other structures. The Ptr necrosis toxin from isolate 86-124 has an isoelectric point near pH 10. Using overlapping proteolytic fragments obtained from the toxin, a sequence of 101 continuous amino acids was obtained, but the amino terminus was blocked and 9 to 16 amino acids could not be sequenced. Secondary structure prediction based on the amino acid sequence indicated a beta-sheet protein with little alpha-helix, which is in agreement with the structure determined 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.