Figure 1.

Clustal W2 multiple sequence alignment of the different PcF Toxin family members. Top panel, alignment of Phytophthora cactorum PcF and other Phytophthora infestans putative protein effectors, identified as SCR70, SCR91, and SCR74. Only the first amino acid sequence of each family sub-group is shown integrally. For the other members only differing residues are shown, while dots (·) represent identical residues. Dashes represent alignment gaps. UniProtKB/TrEMBL accession numbers are indicated in parentheses, except for the SCR74 sequence currently not deposited. The signal peptides, experimentally verified only for PcF¹⁷ or predicted by SignalP (http://www.cbs.dtu.dk/services/SignalP/) for all other members, encompass the first 21 residues. Therefore, mature proteins range from the twenty-second to the last residue shown. Conservation refers to the whole family: same residues are denoted; colon (:) indicates strongly conserved residue; full stop (.) indicates weakly conserved residue. Arrows point to protein species selected for characterization in this work. Bottom panel, alignment of predicted mature recombinant isoforms corresponding to the PcF Toxin family members obtained in this work as described in Materials and Methods. Asterisks (*) indicate residues mutated with respect to wild-type proteins, that is Q1E in the three SCR74 species obtained, and C25E in the not deposited SCR74 species resulting from site-directed mutagenesis. (a), CNBr cleavage sites, resulting in conversion of Met to homoserine (Hs). Gray boxes, the six conserved Cys residues were SS bridged according to the disulfide connectivities of PcF.²² White boxes highlight the two additional cysteines, unique to SCR74 species, predicted to form a fourth disulfide bridge. Underlined, the conserved SK(E/C)C motif identified in this study.