Crystallization of the N-terminal domain of human sex hormone-binding globulin, the major sex steroid carrier in blood

The amino-teminal laminin G-like domain of human sex hormone-binding globul in (SHBG), which contains the steroid-binding site and the dimerization dom ain, has been produced in Escherichia coli, purified to homogeneity and cry stallized in complex with Sa-dihydrotestosterone (DHT) in two different cry stal forms. Native data sets have been collected for tetragonal crystals (s pace group P4(1)22 or P4(3)22; unit-cell parameters a = 52.2, c = 148.4 Ang strom) diffracting to 3.3 Angstrom and trigonal crystals (R32; a = 104.0, c = 84.4 Angstrom) diffracting to better than 1.6 Angstrom. Since both cryst al forms can only accommodate a single monomer in the asymmetric unit and s hare twofold rotational symmetry, it is proposed that the homodimer of this truncated form of SHBG, as observed in ultracentrifugation experiments, di splays C-2 point-group symmetry.