The major coat protein, hexon, from a chimpanzee adenovirus (AdC68) is of interest as a target for vaccine vector modification. AdC68 hexon has been crystallized in the orthorhombic space group C222 with unit cell dimensions of a = 90.8 angstrom, b = 433.0 angstrom, c = 159.3 angstrom, and one trimer (3 x 104,942 Da) in the asymmetric unit. The crystals diffract to 2.1 angstrom resolution. Initial studies reveal that the molecular arrangement is quite unlike that in hexon crystals for human adenovirus. In the AdC68 crystals, hexon trimers are parallel and pack closely in two-dimensional continuous arrays similar to those formed on electron microscope grids. The AdC68 crystals are the first in which adenovirus hexon has molecular interactions that mimic those used in constructing the viral capsid. (c) 2006 Elsevier Inc. All rights reserved.