Opening Image: Surface model of cryptogein complexed to cholesterol.
The very property that makes cholesterol useful in cell membranes, namely, its absolute insolubility in water, requires water-soluble proteins like crytogenin which can bind cholesterol or other sterols and transport them to and from different cells. Cryptogein is such protein. It is secreted by certain fungi and acts as a catalyst to shuttle plant sterols from the membrane of infected plant cells to the pathogen, allowing it to grow.
Cholesterol (CPK model) was substituted for plant sterol in the crystal structure. It binds in the large inner hydrophobic cavity. Hydrophobic sidechains of the protein in van der Waals contact with cholesterol are colored green. the cholesterol molecule to examine the central cavity.