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 identified 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 leaves. 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 determined; this protein consists of 120 amino acid residues, contains 4 cysteines (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 modification occurs. Searches performed by the BLAST program in data banks (Swiss-Prot, EBI, and GenBank(TM)) revealed that this protein is highly homologous with two proteins produced by other Ascomycete fungi. One, produced during infection of wheat leaves, is codified by the snodprot1 gene of Phaeosphaeria nodorum (the causal agent of glume blotch of wheat), whereas the other is the rAsp f13 allergen from Aspergillus fumigatus. Furthermore, the N terminus of cerato-platanin is homologous with that of cerato-ulmin, a phytotoxic protein belonging to the hydrophobin family and produced by Ophiostoma (Ceratocystis) ulmi, a fungus responsible for Dutch elm disease

The 18 kDa cytosolic acid phosphatase from bovine liver has phosphotyrosine phosphatase activity on the autophosphorylated epidermal growth factor receptor

AbstractIn this paper we demonstrate that the cytosofic low-Mr acid phosphatase purified from bovine liver has phosphotyrosine protein phosphatase acitivity on 32P-autophosphorylated epidermal growth factor (EGF) receptor. This activity was significantly inhibited by orthovanadate and p-hydroxymercuribenzoate; the latter result indicates that free sulfhydryl groups are required for phosphotyrosine phosphatase activity. The enzyme was active in a broad pH range, with maximum activity between pH 5.5 and 7.5. The apparent Km for 32P-EGF receptor dephosphorylation was 4 nM. The enzyme appeared to be specific for phosphotyrosine in that it dephosphorylated the autophosphorylated EGF receptor and L-phosphotyrosine, but not 32P-Ser-casein, L-phosphoserine or L-phosphothreonine. These data suggest that the cytosolic low-Mr acid phosphatase might play a regulatory role in EGF receptor-dependent transmembrane signalling