Crystallization and preliminary x-ray diffraction studies of aSFP, a bovine seminal plasma protein with a single CUB domain architecture

Bovine acidic seminal fluid protein (aSFP) is a 12.9 kDa polypeptide of the spermadhesin family built by a single CUB domain architecture. The CUB domain is an extracellular module present in 16 functionally diverse proteins. To determine the three-dimensional structure of aSFP, the protein was crystallized at 21 degrees C by vapor diffusion in hanging drops, using ammonium sulfate, pH 4.7, and polyethyleneglycol 4000 as precipitants, containing 10% dioxane to avoid the formation of clustered crystals. Elongated prismatic crystals with maximal size of 0.6 x 0.3 x 0.2 mm(3) diffract to beyond 1.9 Angstrom resolution and belong to space group P2(1)2(1)2, with cell parameters a = 52.4 Angstrom, b = 41.5 Angstrom, c = 48.2 Angstrom. There is one aSFP molecule per asymmetric unit, which corresponds to a crystal volume per unit molecular mass of 2.04 Angstrom(3)/Da, and analytical ultracentrifugation analysis show that aSFP is a monomeric protein.