Characterization of intertype specific epitopes on adenovirus hexons.

The specification and differentiation of eighteen intertype specific (IT) epitopes of adenovirus hexons defined by monoclonal antibodies are given by two groups of hexon types: on which they are and on which they are not present. The close specificity relationship among some groups of epitopes determined by pairwise analysis according to their presence on the hexon types indicate that they could be continuous (sequential), overlapping or discontinuous (topographic) epitopes. Based on the identification of the hydrophilic regions and the localization of beta-turns sixteen IT epitope sites were predicted on human adenovirus (HAdV) type 2 and nineteen on HAdV-41 hexon's amino acid (aa) sequences beside the type and genus specific ones. The 16 predicted IT epitopes on HAdV-2 hexon show good coincidency with the 14 IT epitopes demonstrated with monoclonal antibodies (MAbs) on this hexon type. The predicted number of common epitopes between HAdV types 2 and 41 also corresponds well with the eight IT epitopes determined by MAbs, but the 17 predicted non-common epitopes indicate the possibility of the existence of more epitopes on these hexon types. The location of the predicted epitopes of HAdV-2 were determined by alignment of their sequence numbers on the three dimensional ribbon representation of the hexon subunit. Most of the predicted IT epitopes were found between the type and genus specific epitopes i.e. in the "upper" regions of pedestal domains P1 and P2 orientated toward the virion surface and in the "lower" part of loop 1 region orientated inside the virion. Two peptides representing potential IT epitopes were synthesized corresponding to residues 309-320 from the "lower" part of loop 1 and 399-408 from the "upper" part of P1 region of HAdV-2 hexon. Antibodies raised against the peptide-carrier conjugates recognized different purified native hexon types in ELISA.