Three‐dimensional solution structure of β cryptogein, a β elicitin secreted by a phytopathogenic fungus phytophthora cryptogea

Cryptogein belongs to a new family of 10‐kDa proteins called elicitins. Elicitins are necrotic and signaling proteins secreted by Phytophthora spp. responsible for the incompatible reaction and systemic hypersensitive‐like necroses of diverse plant species leading to resistance against fungal or bacterial plant pathogens. The solution structure of β cryptogein from Phytophthoru cryptogea fungus was determined by using multidimensional heteronuclear nuclear magnetic resonance spectroscopy. A set of 18 structures was calculated using 1360 NOE‐derived distance restraints and 40 dihedral angle restraints obtained from 3 J HNHα couplings. The RMS deviation from the mean structure is 0.87 ± 0.14 Å for backbone atoms and 1.34 ± 0.14 Å for all the non‐hydrogen atoms of residues 2 to 98. The structure of β cryptogein reveals a novel protein fold, with five helices and a double‐stranded β‐sheet facing an Ω‐loop. One edge of the β‐sheet and the adjacent face of the Ω‐loop form a hydrophobic cavity. This cavity made of highly conserved residues represents a plausible binding site. Residue 13, which has been identified from directed mutagenesis and natural sequence comparison studies as a key amino acid involved in the differential control of necrosis, is surface exposed and could contribute to the binding to a ligand or a receptor. The solution structure is close to the X‐ray structure, with slight differences lightly due to the crystal packing.