The mechanisms by which nonenveloped virions penetrate the endosomal membrane to deliver their genome to the cytoplasm or nucleus remains poorly defined. An understanding of this early step in viral infection could provide a viable target for antiviral therapy or could be exploited for enhanced cytosolic delivery of therapeutically relevant macromolecules. Thus the goal of this research is to develop a working model for the structural basis for membrane penetration using adenovirus (Ad) as a model system. It is thought that the low pH of early endosomes facilitates a conformational change in the Ad capsid that primes it for interaction with the endosomal membrane. We will therefore describe the pH-dependent structural changes in the Ad capsid in terms of gross changes in the quaternary structure of the capsid, conformational changes in individual capsid proteins and exposure of hydrophobic regions of the virus capsid. These pH dependent structural changes will be correlated with the ability of the Ad capsid to facilitate virion association with mode] liposomal membranes and mediate disruption of these membranes. The influence of the composition of the lipid membrane in terms of net charge, intrinsic membrane curvature and fluidity as well as the presence or absence of alphaV integrins on membrane association/disruption will also be addressed. Finally, Ad proteins and protein domains that interact with membranes will be identified by photo labeling with a membrane embedded photoreactive probe. Once identified, recombinant forms of the membrane interacting proteins will be produced and assessed for their ability to interact with model membranes and disrupt biological membranes in cell culture models. ? ?