Purification, characterization, and amino acid sequence of cerato-platanin, a new phytotoxic protein from Ceratocystis fimbriata f. sp platani

A new phytotoxic protein (cerato-platanin) of about 12.4 kDa has been ident ified in culture filtrates of the Ascomycete Ceratocystis fimbriata f. sp, platani, the causal agent of canker stain disease. The toxicity of the pure protein was bioassayed by detecting the inducing necrosis in tobacco leave s. The pure protein also elicited host synthesis of fluorescent substances in tobacco and plane (Platanus acerifolia) leaves. We purified the protein from culture medium to homogeneity, Its complete amino acid sequence was de termined; this protein consists of 120 amino acid residues, contains 4 cyst eines (S-S-bridged), and has a high percentage of hydrophobic residues. The molecular weight calculated from the amino acid sequence agrees with that determined by mass spectrometry, suggesting that no post-transnational modi fication occurs. Searches performed by the BLAST program in data banks (Swi ss-Prot, EBI, and GenBank(TM)) revealed that this protein is highly homolog ous with two proteins produced by other Ascomycete fungi, One, produced dur ing infection of wheat leaves, is codified by the snodprot1 gene of Phaeosp haeria nodorum (the causal agent of glume blotch of wheat), whereas the oth er is the rAsp f13 allergen from Aspergillus fumigatus. Furthermore, the N terminus of cerato-platanin is homologous with that of cerato-ulmin, a phyt otoxic protein belonging to the hydrophobin family and produced by Ophiosto ma (Ceratocystis) ulmi, a fungus responsible for Dutch elm disease.