Four homogeneous proteins (Cw18, Cw20, Cw21, Cw22) were isolated from etiolated barley leaves by extraction of the insoluble pellet from a Tris-HCl (pH 7.5) homogenate with 1.5 M LiCl and fractionation by reverse-phase high-performance liquid chromatography. All 4 proteins inhibited growth of the pathogen Clavibacter michiganensis subsp. sepedonicus (EC50s = 1-3 x 10(-7) M) and had closely related N-terminal amino acid sequences. The complete amino acid sequences of proteins Cw18 and Cw21 were determined and found to be homologous to previously described, non-specific lipid transfer proteins from plants (32-62% identical positions). The proteins also inhibited growth of the bacterial pathogen Pseudomonas solanacearum (EC50s = 3-6 x 10(-7) M) and the fungus Fusarium solani (EC50s = 3-20 x 10(-6) M). A homologous protein from maize leaves (Cw41) was purified in a similar manner and also found to have inhibitory properties. A synergistic effect against the fungus was observed when protein Cw21 was combined with thionins. A defense role for non-specific lipid transfer proteins from plants is proposed.
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Molina et al. (1993) studied this question.