Hexagonal crystalline arrays of adenovirus type 1 hexons

Separated, highly purified and concentrated adenovirus type 1 soluble hexon capsomers were crystallized by dialysis against 0.5 M acetate buffer. The crystallization process was followed electron microscopically. In the early phase of the crystallization, groups of a few hexons began to appear, then the two-dimensional crystal lattices grew gradually to a size of 1-2 micron. Simultaneously three-dimensional crystals of tetrahedral and prismatic shapes developed. The hexons in the two-dimensional crystal lattice formed regulator dense arrays corresponding to the hexagonal packing. Analysis of the crystal structure revealed 15-20% local irregularity (short range disorder) and about 10% deviation in the values of the lattice constant if determined from three different directions. The average lattice constant values showed considerable differences in different preparations. Angles formed by non-parallel hexon rows deviated by a few degrees from the regular hexagonal order. Consequently, the position of the hexons in dense two-dimensional crystals was found slightly skew and irregular, although each unit stayed within a certain distance as compared to its equilibrium position defined theoretically in the network. Dislocations were frequently found to disturb the regular arrays. The extra hexon row developing between two rows deverted them from their original direction. At these sites the crystal lattice slanted and the dense array of the hexons loosened. High resolution electron microscopy revealed fine linking structures between the hexons. In several cases the aggregated hexons failed to show a ring-like appearance, they were situated in lying--profile--position and the hexon-building polypeptide fibres became visible. The diameters of the hexons and the distance between them were measured in three directions and the size of the hexon-building polypeptides was determined as well.