Arrangement of hexons and polypeptide subunits in the adenovirus capsid

With direct analysis of electron micrographs and with Markham's rotational integration technique we have demonstrated that in the adenovirus capsid the triangular profile of the hexon-end facing are formed by one polypeptide each and the sides by two neighbouring polypeptides. The mutual rotational and spatial orientation of the three hexon polypeptide subunits has been determined in relation to each other and to the pentons. Two polypeptides of the peripentonal hexons are oriented towards the penton. A "one-to-one" pattern was found in relation to two peripentonal hexons, "one-to-two" to two of the three neighbouring hexons and "two-to-two" to one hexon. "One-to-two" orientation is the general rule in the GONs. The mutual orientation between the hexons of the neighbouring GONs being in connection with each other and that of the polypeptide subunits of the peripentonal hexons is characterized by the regular alternation of the "one-to-two", "one-to-one" and "two-to-two" orientation. The mutual orientation between the hexons at different points of the capsid has been studied in model experiments and was characterized by the angle enclosed by the longitudinal axis of the given hexon and that of the other hexon in open position towards the virion surface, if the longitudinal axis of the hexons of the triangular faces are perpendicular to the plane of the face and those of the edge-hexons perpendicular to the plane of the edge and the longitudinal axis of the penton faces in radial direction the centre of the virion. In this way the longitudinal axes of the peripentonal hexons enclose with that of the penton an angle of approximately 32 degrees and with each other approximately 36 degrees. The longitudinal axis of the edge-forming hexons shows a deviation of approximately 21 degrees in relation to the longitudinal axes of hexons situated on the neighbouring triangular faces. We present on a tentative virus model the mutual rotational and spatial orientation of all the polypeptide subunits of the adenovirus-building hexon capsomers. This corresponds to the two-, three- and fivefold rotational symmetry characteristic of the icosahedral capsid.