Structure of adenovirus fibre. I. Analysis of crystals of fibre from adenovirus serotypes 2 and 5 by electron microscopy and X-ray crystallography.

An analysis by electron microscopy in amorphous ice and X-ray diffraction of four types of three-dimensional crystals of adenovirus fibre is presented. Fibre from adenovirus type 2 (Ad2) crystallizes in two forms depending on whether it is native or cleaved near the N terminus at Tyr17. Fibre from Ad5 also crystallizes in two forms, both of which contained fibre cleaved at Tyr17. Analysis of the packing of the fibres in each of these crystals suggests that the overall length of the fibre may be considerably longer (about 350 to 370 A) than previously reported. Crystals of cleaved Ad2 fibre are of sufficient quality to be characterized by X-ray diffraction. They are of space group C2 and cell dimensions a = 134.4 A, b = 77.6 A, c = 539.4 A, beta = 92.7 degrees. These crystals are remarkable in that, despite being monoclinic, the ab plane forms a perfect hexagonal lattice. This is explained by a trigonal packing of the trimeric fibre heads in the crystal. A similar feature is found for one type of Ad5 crystal, although the hexagonal lattice is 12% smaller. The crystals of cleaved Ad2 show very strong meridional intensity at a Bragg spacing of 4.4 A and weaker diffuse intensity corresponding to layer-lines of spacing 26.4 A. This must reflect the quasiperiodicity of the structure of the fibre shaft, which is apparent in the primary sequence. The occurrence of these features combined with the new determination of the length of the fibre (see also the accompanying paper) require a reappraisal of the cross-beta model of the fibre shaft proposed by Green et al.