NEW CRYSTAL FORM AND CRYSTAL STRUCTURE OF S100B FROM BOVINE BRAIN AT 2.5 Å RESOLUTION. Hiroyoshi Matsumura*, Tomoo Shiba**, Tsuyoshi Inoue*, Shigeharu Harada** and Yasushi Kai*. *Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan; **Faculty of Pharmaceutical Sciences, University of Tokyo,Bunkyou-ku, Tokyo 113.

S100b belongs to S100 proteins family and consists of a dimer of two S100[[beta]] subunits ( 91 amino acid residues; MW 10,500 ) including two EF-hand ( helix-loop-helix motif ) calcium binding sites. S100b is sensitive to the concentration of Ca²⁺ and changes its conformation and activity in the form of dimer.

We have grown a new crystal of S100b from bovine brain and determined its three dimensional structure by X-ray diffraction method at 2.5 Å resolution. The crystal belongs to an orthorhombic system of space group C222₁. The unit-cell dimensions are determined as a= 36.18, b= 89.75 and c= 58.36 Å. The asymmetric unit of the crystal lattice includes one S100[[beta]] subunit with a Vm value of 2.22 ų / Da. The crystal structure of S100b was determined by the molecular replacement method using calbindin D_9k in calcium binding state as starting structure model. The crystallographic R-factor of the structure refined by X-PLOR is 0.19.

REFERENCE

1.Isobe,T.,Okuyama,T. (1978) Eur.J.Boichem 89, 379-388

2.Doletha M.E. Szebenyi and Keith Moffat (1985)J.Biological Chemistry 261, 8761-8777