An in situ AFM investigation of catalase crystallization

Surface morphology, growth and dissolution of crystals of the protein catalase were studied by in situ atomic force microscopy (AFM). Growth of the (001) face of catalase crystals proceeds in alternating patterns by two-dimensional nucleation and successive deposition of two distinctive growth layers, each having a step height equal to half the unit cell parameter. Shapes of two-dimensional nuclei exhibit strong asymmetry due to directional anisotropy in step rates. The shapes of islands on successive layers are related by two-fold rotation axes along the [001] direction. Lattice resolution AFM images of the molecular structure of sequential surface layers were recorded. Adsorption of large three-dimensional clusters of molecules was also observed to occur on the surfaces of catalase crystals. These clusters developed into either properly aligned multilayer stacks or misaligned microcrystals. Incorporation of misoriented microcrystals as large as 50 x 3 x 0.1 mu m(3) proceeded without formation of defects. Upon incorporation of microcrystals and subsequent deposition of new layers on the surface of a growing crystal, impressions with depths of up to 0.4 of the growth layer thickness formed due to misfits between the lattices of the microcrystals and those of the growth layers. This produced elastic deformations in growth layers of approximate to 0.6%. (C) 1997 Elsevier Science B.V.