Electron microscopic studies on the crystallization of adenovirus hexon capsomers

Highly purified soluble adenovirus type 1 hexons were crystallized by dialyzing against 0.5 M acetate buffer, pH 4.5, for 3 days. Crystals of tetrahedral shape were formed after storage at 4 degrees within 1--10 days and ranged in size from 0.01 to 0.1 mm. In early phase of crystallization, diffusely dispersed hexons were observed by electron microscopy. Later, continuous monolayers of two-dimensional hexon paracrystalline arrays developed. Direct analysis of the electron micrographs and their optical diffraction patterns showed that the structure of the dense two-dimensional crystalline arrays of hexon capsomers was characterized by slightly skew and irregular hexagonal packing. Multilayered microcrystals with regular linear internal structure were also found. In addition, unique forms of aggregated hexons, such as holey hexon lattice and filamentous forms, were also found.