A New Crystal Form of Proteinase A, a Non-Pepsin-Type Acid Proteinase from Aspergillus niger var. macrosporus1

Abstract

Proteinase A from Aspergillus niger var. macrosporus is a non-pepsin-type acid proteinase, whose catalytic residues and mechanism remain to be elucidated. A new form of proteinase A crystals more suitable for crystallography than that obtained previously was prepared from an ammonium sulfate solution at pH 3.5 by the hanging-drop vapor diffusion method. The space group of the crystals was P2(1)2(1)2(1), with unit cell dimensions of a = 69.75 +/- 0.06 A, b = 87.55 +/- 0.05 A, and c = 60.83 +/- 0.04 A. On the assumption of two enzyme molecules per asymmetric unit, the calculated volume to unit protein mass ratio (Vm) was 2.08 A3/Da. By assuming the specific volume to be 0.74 cm3/g, the solvent content (Vso1) was estimated to be 41%, i.e., much larger than that of the crystal form obtained previously at pH 2.0 (Vso1 = 26%). Diffraction data were collected up to a resolution higher than 1.6 A, using the Weissenberg camera for macromolecular crystallography with synchrotron radiation.