The 2.1 Å structure of an elicitin‐ergosterol complex: A recent addition to the Sterol Carrier Protein family

Abstract

Elicitins, produced by most of the phytopathogenic fungi of the genus Phytophthora, provoke in tobacco both remote leaf necrosis and the induction of a resistance against subsequent attack by various microorganisms. Despite the recent description of the three-dimensional crystal structure of cryptogein~CRY!, the molecular basis of the interactions between Phytophthora and plants largely remains unknown. The X-ray crystal structure, refined at 2.1 Å, of a ligand complexed, mutated CRY, K13H, is reported. Analysis of this structure reveals that CRY is able to encapsulate a ligand that induces only a minor conformational change in the protein structure. The ligand has been identified as an ergosterol by gas chromatographic analysis coupled with mass spectrometry analysis. This result is consistent with biochemical data that have shown that elicitins are a distinct class of Sterol Carrier Proteins~SCP!. Data presented here provide the first structural description of the pertinent features of the elicitin sterol interaction and permit a reassessment of the importance of both the key residue 13 and the mobility of the omega loop for the accessibility of the sterol to the cavity. The biological implications thereof are discussed. This paper reports the first structure of a SCP0sterol complex.

Mediation of Elicitin Activity on Tobacco Is Assumed by Elicitin-Sterol Complexes

“…On the contrary, the Y47G replacement strongly increases this parameter. This indicates that either the thrust role of the aromatic ring of tyrosine (or phenylalanine) or the van der Waals interactions with the sterol are of prime importance in the stability of the sterolelicitin complex, as previously suggested by structural analysis (Boissy et al, 1999).…”

“…Clear conformational changes were observed between void and ergosterol-complexed cryptogein (Boissy et al, 1999), which could explain how sterol-loading "activates" elicitins allowing them to bind to high-affinity sites.…”

“…This could be explained by the behavior of this tyrosine residue during complex formation. In the native cryptogein, it stays in the hydrophobic cavity (Boissy et al, 1996;Fefeu et al, 1997;Gooley et al, 1998), whereas in the sterol-loaded cryptogein, it rotates and becomes exposed to solvent (Boissy et al, 1999; Figure 1). The tyrosine residue could be in contact with the aqueous environment, because of its hydrophilic hydroxyl, whereas the hydrophobic phenylalanine residue could not.…”

“…The aim of the mutagenesis was to alter the sterol-loading properties of cryptogein and was based on the crystal structure of an engineered cryptogein-ergosterol complex (Boissy et al, 1999). Interaction between the protein and ergosterol involves several residues of the cryptogein hydrophobic core, among which tyrosine residues are the most represented (Boissy et al, 1999).…”

“…These amino acids were chosen for their characteristics as highlighted by structural observations (Boissy et al, 1996(Boissy et al, , 1999. Tyrosine-47 residue is involved in the sole hydrogen bond between the protein core and the sterol hydroxyl (Figure 1).…”