CRYSTALLIZATION OF HUMAN METHYLAMINE-TREATED COMPLEMENT-C3 AND COMPLEMENT-C3B

Human methylamine-treated complement C3 (C3-MA) and C3b (C3b-MA) have been crystallized using ammonium sulfate as precipitant. The crystals of the two compounds are morphologically indistiguishable though they belong to different space groups. We show that only minor alterations in packing are responsible for the change in space group. Crystals of C3-MA are tetragonal [P4(1(3))22, a = b = 135, c = 610 angstrom] with two molecules per asymmetric unit. Crystals of C3b-MA are also tetrago nal [P4(1(3))2(1)2, a = b = 191, c = 610 angstrom] with four molecules per asymmetric unit. The maximum diffraction observed is 7.7 angstrom at cryogenic temperature using synchrotron radiation.