Purification and antipathogenic activity of lipid transfer proteins (LTPs) from the leaves of Arabidopsis and spinach.

Two homogeneous proteins active in vitro against the bacterial pathogen Clavibacter michiganensis subsp. sepedonicus were obtained from a crude cell-wall preparation from the leaves of Columbia wild-type Arabidopsis. The N-terminal amino acid sequences of these proteins allowed their identification as lipid transfer proteins (LTP-a1, LTP-a2); the LTP1-a1 sequence was identical to that deduced from a previously described cDNA (EMBL M80566) and LTP-a2 was quite divergent (44% identical positions). These proteins were not detected in the cytoplasmic fraction by Western-blot analysis. Proteins LTP-s1 and LTP-s2 were similarly obtained from spinach leaves; LTP-s1 was 91% identical to a previously purified spinach LTP (Swiss Prot P10976), and LTP-s2 was moderately divergent (71% identical positions). About 1/3 of the total LTPs were detected in the cytoplasmic fraction from spinach by Western-blot analysis. Concentrations of these proteins causing 50% inhibition (EC-50) were in the 0.1-1 microM range for the bacterial pathogens C. michiganensis and Pseudomonas solanacearum and close to 10 microM for the fungal pathogen Fusarium solani.