Inter- and intrahexonal connections between adenovirus hexon polypeptides in the two-dimensional crystalline array

Interpretation of electron micrographs of adenovirus hexon arrays using a crystallographic molecular model

Two types of two-dimensional arrays of purified adenovirus type 2 hexon have been obtained and analyzed by Fourier filtration of their electron micrographs. One array contained continuously close-packed hexons, distributed on a hexagonal p3 lattice, with a unit cell dimension of 94 +/- 2 A. The other array contained close-packed hexons with a regular absence, so that rings of six hexons related by sixfold symmetry formed a p6 unit cell. The cell dimension of the hexagonal array was 153 +/- 3 A, with neighboring hexons separated by 88 +/- 2 A. Smaller p6 arrays were also formed by hexons freed from complete virions on the microscope grid by treatment with distilled water. A molecular model of hexon, known from the X-ray crystallographic structure, was used to interpret Fourier-filtered images of the arrays, and to determine the relative orientations of the hexon molecules. The hexon-hexon interaction in the p3 array is that found in the virion facet, whereas that in the p6 array is a planar form of the interaction between peripentonal hexons around the vertex.

Mutual orientation of peripentonal hexons and polypeptide subunits in the adenovirus capsid

The mutual rotational orientation of the three hexon polypeptide subunits of the peripentonal hexons has been determined in relation to each other, to the penton and to the neighbouring hexons. The possible mutual orientation of all the polypeptide subunits of the adenovirus-building hexon capsomers are presented on a tentative virus model.

Electron microscopic studies on the connections between capsomers in the adenovirus capsid

Electron microscopic observation of negatively stained virions suggests that the interhexonal spaces within the adenovirus capsid are bridged by interhexonal connective elements. Similar connections are also detected between pentons and the five peripentonal hexons. Examinations of electron micrographs by Markham's rotational integration technique reveals the presence of a regular network of the connective elements between the capsomers in the whole capsid. The length of these connections corresponds to about one-third of the diameter of the hexons. The connections consist of two approximately parallel elements, thus every hexon is joined to its six nearest neighbours by 12 connections. A possible mutual orientation pattern of the connective elements in the whole capsid is presented on a tentative virus model.