Mutual orientation of adenovirus hexon polypeptides in a two-dimensional crystalline array.

Three profiles of hexons were detected om two-dimensional adenovirus crystalline arrays: (i) approximately ringwise closed hexons with a roundish hole in their centres and with 2-4 electron dense spots in the wall of the rings; (ii) hexons, consisting of three approximately oblong polypeptide enclosing a triangular hole; (iii) triangular hexons, containing three main polypeptides with an Y-shaped slit, instead of a hole, in their centres. Following the examination of directly or computer corrected electron micrographs a tentative model has been developed on the possible mutual "rotation" orientation of hexon polypeptides within the two-dimensional crystalline array. The position of hexons is such that the longer side of a polypeptide of each hexon is next to the end of two polypeptides of its neighbouring hexon, i.e. one polypeptide is linked to two other ones. An irregularity evolves in this "one-to-two" linkage system by the rotation of a hexon, the maximum rotation being 60% degrees, as follows from the hexon's threefold symmetry. The presence of lying hexons and of hexons of different contours, points to irregularities in "vertical" orientation, with the turn reaching even 90 degrees or 180 degrees, i.e. the hexons might be connected in such a way that their originally external or internal parts are facing identical directions.