3-DIMENSIONAL SOLUTION STRUCTURE OF BETA-CRYPTOGEIN, A BETA-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 Phytophtho ra spp. responsible for the incompatible reaction and systemic hyperse nsitive-like necroses of diverse plant species leading to resistance a gainst fungal or bacterial plant pathogens. The solution structure of beta cryptogein from Phytophthora cryptogea fungus was determined by u sing multidimensional heteronuclear nuclear magnetic resonance spectro scopy. A set of 18 structures was calculated using 1360 NOE-derived di stance restraints and 40 dihedral angle restraints obtained from (3)J( HNH alpha) couplings. The RMS deviation from the mean structure is 0.8 7 +/- 0.14 Angstrom for backbone atoms and 1.34 +/- 0.14 Angstrom for all the non-hydrogen atoms of residues 2 to 98. The structure of beta cryptogein reveals a novel protein fold, with five helices and a doubl e-stranded beta-sheet facing an Omega-loop. One edge of the beta-sheet and the adjacent face of the Omega-loop form a hydrophobic cavity. Th is cavity made of highly conserved residues represents a plausible bin ding site. Residue 13, which has been identified from directed mutagen esis and natural sequence comparison studies as a key amino acid invol ved in the differential control of necrosis, is surface exposed and co uld contribute to the binding to a ligand or a receptor. The solution structure is close to the X-ray structure, with slight differences lig htly due to the crystal packing.