Crystallization and preliminary crystallographic analysis of sfericase: A Bacillus sphaericus calcium-dependent serine proteinase

Sfericase is an important intracellular proteinase produced by Bacillus sphaericus in the, stationary phase of growth. It is a Ca²⁺-dependent serine proteinase with optimal activity at pH 9.0 to 9.3. The molecular mass of sfericase is 32 kDa, as determined by sedimentation equilibrium. It seems to be involved in the interplay of various elements of the mosquitocidal activity of B. sphaericus, and hence is important for biological mosquito control. Sfericase significantly reduces viscosity of human pathological bronchial secretions and has recently shown good clinical effects in treatment of bronchitis, pneumonia and sinusitis. This enzyme was isolated from B. sphaericus and single crystals were obtained by the hanging drop vapor diffusion method. The crystals belong to the monoclinic space group P2, with cell dimensions of a = 46.94 å, b = 64.55 å, c = 86.23 å and β = 95.4°. These crystals are mechanically strong, they are stable in the X-ray beam and they diffract to better than 1.8 å resolution. The cell dimensions are consistent with four molecules per unit cell and two molecules in the asymmetric unit. A complete native data set to 1.77 å resolution has been collected on a Rigaku R-AXIS-IIc Imaging Plate Detector system and a heavy-atom derivative search is presently in progress.