Defining CAR as a cellular receptor for the avian adenovirus CELO using a genetic analysis of the two viral fibre proteins

The coxsackievirus and adenovirus receptor (CAR) is a high affinity recepto r used by adenoviruses, including adenovirus type 5 (Ad5). The adenovirus f ibre molecule bears the high affinity cell binding domain of Ad 5, allowing virions to attach to CAR. The avian adenovirus CELO displays two fibre mol ecules on its capsid and it was logical to expect that the cell binding fun ctions of CELO might also reside in one or both of these fibres. We had pre viously shown that the cell binding properties of CELO resemble Ad5, sugges ting that the two viruses use similar receptors. Experiments with CAR-defic ient CHO cells and CHO cells modified to express CAR demonstrated that CELO has CAR-dependent transduction behaviour like Ad5. Mutations were introduc ed into the CELO genome to disrupt either the long fibre 1 or the short fib re 2, A CELO genome with fibre 2 disrupted did not generate virus, demonstr ating that fibre 2 is essential for some stage in virus growth, assembly or spread. However, a CELO genome with disrupted fibre 1 gene produced virus (CELOdF1) that was capable of entering chicken cells, but had lost both the ability to efficiently transduce human cells and the CAR-specific transduc tion displayed by wild-type CELO, The ability of CELOdF1 to transduce chick en cells suggests that CELOdF1 may still bind, probably via fibre 2, to a r eceptor expressed on avian but not mammalian cells. CELOdF1 replication was dramatically impaired in chicken embryos, demonstrating that fibre 1 is im portant for the in vivo biology of CELO.