The phytotoxic protein PcF (Phytophthora
cactorum-Fragaria) is a 5.6-kDa cysteine-rich, hydroxyproline-
containing protein that is secreted in limited amounts by P. cactorum, an oomycete pathogen of
tomato, strawberry and other relevant crop plants. Although we have shown that pure PcF triggers
plant reactivity, its mechanism of action is not yet understood. Here we show that PcF, like other
known fungal protein elicitors involved in pathogen-plant interaction, stimulates the activity of
the defense enzyme phenylalanine ammonia a key step in understanding the mechanism of action of
PcF at a molecular level is knowledge of its three-dimensional structure, we overexpressed this
protein extracellularly in Pichia pastoris. The preliminary
structural and functional characterization of a recombinant PcF homologue, N4-rPcF, is reported.
Interestingly, although N4-rPcF is devoid of proline hydroxylation and has four additional
amino acid residues attached to its N terminus, its secondary structure and biological activity are
indistinguishable from wild-type PcF.