PROTEIN LIGANDS OF THE HUMAN ADENOVIRUS TYPE-2 OUTER CAPSID IDENTIFIED BY BIOPANNING OF A PHAGE-DISPLAYED PEPTIDE LIBRARY ON SEPARATE DOMAINS OF WILD-TYPE AND MUTANT PENTON CAPSOMERS

A filamentous phage-displayed random hexapeptide library was screened on the adenovirus type 2 (Ad2) penton capsomer and its separate domain s, penton base, full-length fiber, fiber shaft and fiber knob. Affinit y supports were designed to immobilize the penton ligate with a prefer red orientation, via immunoadsorption to pre-coated antibody. Three cl asses of phagotopes were distinguished in the eluates from the penton and fiber domains, (i) The first class represented peptide sequences i dentified in certain Ad2 capsid proteins, protein IIIa, protein pVIII, penton base and penton fiber. Data from specific ligand elution of ph ages bound to fiber and penton base wild-types and mutants suggested t hat the region overlapping the RLSNLLG motif at residues 254-260 in th e penton base and the FNPVYP motif at residues 11-16 in the fiber tail formed mutual interacting sites in the penton capsomer, (ii) The seco nd class consisted of phagotopes homologous to peptide sequences found in host cell membrane proteins involved in receptor or adhesion funct ions, One of the most abundant species corresponded to a conserved mot if present in the beta-strand B of type III modules of human fibronect in. In addition, phages which were screened for their failure to bind to penton base RGD mutants were found to carry consensus motifs to pep tide sequences present in the RGD recognition site of human integrin b eta subunits, (iii) The third class comprised peptide motifs common to both viral and cellular proteins, suggesting that a mechanism of liga nd exchange could occur during virus entry and uncoating, and virus as sembly and release.