Adenovirus hexon protein, molecular model. Hexon proteins are part of the protein coat or shell (capsid) of adenoviruses. In viruses, the capsid encloses the genetic material and in adenoviruses is icosahedral in shape (20-sided). There are 12 hexon trimers on each of the 20 faces of the icosahedral capsid, with nine central hexons and three peripheral ones involved in forming the vertex structures. The total number of hexon trimers is 240. This hexon protein is from human adenovirus 2 (hAd2). Adenoviruses cause infections of the upper respiratory tract, causing cold-like symptoms.