A triple β-spiral in the adenovirus fibre shaft reveals a new structural motif for a fibrous protein

Human adenoviruses1 are responsible for respiratory, gastro-enteric and ocular infections2 and can serve as gene therapy vectors3. They form icosahedral particles with 240 copies of the trimeric hexon protein arranged on the planes and a penton complex at each of the twelve vertices. The penton consists of a pentameric base, implicated in virus internalization4, and a protruding trimeric fibre, responsible for receptor attachment5. The fibres are homo-trimeric proteins containing an amino-terminal penton base attachment domain, a long, thin central shaft and a carboxy-terminal cell attachment or head domain. The shaft domain contains a repeating sequence motif with an invariant glycine or proline and a conserved pattern of hydrophobic residues6. Here we describe the crystal structure at 2.4 Å resolution of a recombinant protein containing the four distal repeats of the adenovirus type 2 fibre shaft plus the receptor-binding head domain. The structure reveals a novel triple β-spiral fibrous fold for the shaft. Implications for folding of fibrous proteins (misfolding of shaft peptides leads to amyloid-like fibrils) and for the design of a new class of artificial, silk-like fibrous materials are discussed.