Crystallization and preliminary X-ray crystallographic studies on the fungal immunomodulatory protein Fve from the golden needle mushroom (Flammulina velutipes)

The fungal immunomodulatory protein from the edible golden needle mushroom (Flammulina velutipes), designated Fve, is a single polypeptide consisting of 114 amino-acid residues. It is believed to trigger the mitogenic proliferation of T lymphocytes and Th1 cytokine production. Here, it is demonstrated that Fve forms a homodimer in nature. In order to understand the relationship between its structure and function, Fve was crystallized using the hanging-drop method; the protein formed well diffracting crystals within 3-5 d in 2.5% PEG 400, 2.0 M ammonium sulfate and 0.1 M Tris base buffer pH 8.5. The space group of the Fve crystals is either P4₃2₁2 or P4₁2 ₁2, with unit-cell parameters a =- b = 96.92, c = 61.42 Å. The crystal contains two molecules per asymmetric unit and diffracts to 1.4 Å resolution when exposed to synchrotron radiation.