X-ray crystallographic and biochemical characterization of single crystals formed by proteolytically modified human fibrinogen.

Large single crystals (0.7 mm X 0.4 mm X 0.3 mm) of human fibrinogen, modified with a crude exoprotease from Pseudomonas aeruginosa, have been obtained. The crystals are orthorhombic, space group P212121, with a = 9.5 +/- 0.1 nm, b = 11.1 +/- 0.1 nm, c = 44.0 +/- 0.4 nm. Their X-ray diffraction patterns extend to beyond 1.0 nm resolution. The asymmetric unit contains one fragment of 245 kDa molecular mass made up of an intact gamma chain, a slightly shortened beta chain and an N-terminal part (about one-third) of the alpha chain. In electron micrographs of rotary-shadowed samples the crystallized particles are very similar in size and shape to the well-known trinodular form of native fibrinogen. From the unit-cell dimensions and the intensity pattern a model is proposed in which the molecules consist of two halves related by a local twofold rotation axis, and are aligned with a displacement of multiples of 1/4 of their length giving a pseudohexagonal packing scheme.