ANALYSIS OF 15 ADENOVIRUS HEXON PROTEINS REVEALS THE LOCATION AND STRUCTURE OF 7 HYPERVARIABLE REGIONS CONTAINING SEROTYPE-SPECIFIC RESIDUES

The first full-length hexon protein DNA and deduced amino acid sequenc es of a subgenus D adenovirus (AV) were determined from candidate AV48 (85-0844), Comprehensive comparison of this sequence with hexon prote in sequences from human subgenera A, B, C, D, F, bovine AV3, and mouse AV1 revealed seven discrete hypervariable regions (HVRs) among the 25 0 variable residues in loops 1 and 2, These regions differed in length between serotypes, from 2 to 38 residues, and contained >99% of hexon serotype specific residues among human serotypes, Alignment with the published crystal structure of AV2 established the location and struct ure of the type-specific regions, Five HVRs were shown to be part of l inear loops on the exposed surfaces of the protein, analogous to the s erotype-specific loops or ''puffs'' in picornavirus capsid proteins. T he HVRs were supported by a common framework of conserved residues, of which 68 to 75% were hydrophobic. Unique sequences were limited to th e seven HVRs, so that one or more of these regions contain the type-sp ecific neutralization epitopes, A neutralizing AV48 hexon-specific ant iserum recognized linear peptides that corresponded to six HVRs by enz yme immunoassay. Affinity-purification removal of all peptide-reactive antibodies did not significantly decrease the neutralization titer, f luted peptide-reactive antibodies did not neutralize, Human antisera t hat neutralized AV48 did not recognize linear peptides, Purified trime ric native hexon inhibited neutralization, but monomeric heat denature d hexon did nut, We conclude that the AV48 neutralization epitope(s) i s complex and conformational.