HUMAN ADENOVIRUS SEROTYPE-3 AND SEROTYPE-5 BIND TO 2 DIFFERENT CELLULAR RECEPTORS VIA THE FIBER HEAD DOMAIN

The adenovirus fiber protein is responsible for attachment of the viri on to cell surface receptors. The identity of the cellular receptor wh ich mediates binding is unknown, although there is evidence suggesting that two distinct adenovirus receptors interact with the group C (ade novirus type 5 [Ad5]) and the group B (Ad3) adenoviruses. In order to define the determinants of adenovirus receptor specificity, we have ca rried out a series of competition binding experiments using recombinan t native fiber polypeptides from Ad5 and Ad3 and chimeric fiber protei ns in which the head domains of Ad5 and Ad3 were exchanged. Specific b inding of fiber to HeLa cell receptors was assessed with radiolabeled protein synthesized in vitro, and by competition analysis with baculov irus-expressed fiber protein. Fiber produced in vitro was found as bot h monomer and trimer, but only the assembled trimers had receptor bind ing activity. Competition data support the conclusion that Ad5 and Ad3 interact with different cellular receptors. The Ad5 receptor distribu tion on several cell lines was assessed with a fiber binding flow cyto metric assay. HeLa cells were found to express high levels of receptor , while CHO and human diploid fibroblasts did not. A chimeric fiber co ntaining the Ad5 fiber head domain blocked the binding of Ad5 fiber bu t not Ad3 fiber. Similarly, a chimeric fiber containing the Ad3 fiber head blocked the binding of labeled Ad3 fiber but not Ad5 fiber. In ad dition, the isolated Ad3 fiber head domain competed effectively with l abeled Ad3 fiber for binding to HeLa cell receptors. These results dem onstrate that the determinants of receptor binding are located in the head domain of the fiber and that the isolated head domain is capable of trimerization and binding to cellular receptors. Our results also s how that it is possible to change the receptor specificity of the fibe r protein by manipulation of sequences contained in the head domain. M odification or replacement of the fiber head domain with novel ligands may permit adenovirus vectors with new receptor specificities which c ould be useful for targeted gene delivery in vivo to be engineered.