Crystal structures of the free and sterol-bound forms of β-cinnamomin

The crystal structure of the elicitin β-cinnamomin (β-CIN) was determined in complex with ergosterol at 1.1 Å resolution. β-CIN/ergosterol complex crystallized in the monoclinic space group P21, with unit cell parameters of a = 31.0, b = 62.8, c = 50.0 Å and β = 93.4° and two molecules in the asymmetric unit. Ligand extraction with chloroform followed by crystallographic analysis yielded a 1.35 Å structure of β-CIN (P43212 space group) where the characteristic elicitin fold was kept. After incubation with cholesterol, a new complex structure was obtained, showing that the protein retains, after the extraction procedure, its ability to complex sterols. The necrotic effect of β-CIN on tobacco was also shown to remain unchanged. Theoretical docking studies of the triterpene lupeol to β-CIN provided an explanation for the apparent inability of β-CIN to bind this ligand, as observed experimentally.