Structure of β‐cinnamomin, a protein toxic to some plant species

Phytophthora and Pythium species are among the most aggressive plant pathogens, as they invade many economically important crops and forest trees. They secrete large amounts of 10 kDa proteins called elicitins that can act as elicitors of plant defence mechanisms. These proteins may also induce a hypersensitive response (HR) including plant cell necrosis, with different levels of toxicity depending on their pI. Recent studies showed that elicitins function as sterol carrier proteins. The crystallographic structure of the highly necrotic recombinant β‐cinnamomin (β‐CIN) from Phytophthora cinnamomi has been determined at 1.8 Å resolution using the molecular‐replacement method. β‐CIN has the same overall structure as β‐cryptogein (β‐CRY), an elicitin secreted by Phytophthora cryptogea , although it shows a different surface electrostatic potential distribution. The protein was expressed in Pichia pastoris and crystallized in the triclinic space group with two monomers in the asymmetric unit. The interface formed by these two monomers resembles that from β‐CRY dimer, although with fewer interactions.