Intrinsic Structural Disorder in Adenovirus E1A: a Viral Molecular Hub Linking Multiple Diverse Processes

Viruses are obligate intracellular parasites. Their genomes are not large enough to encode all the functions required to independently produce progeny; hence, viruses are absolutely dependent on host cell functions. Mechanistically, these host cell processes in eukaryotes are founded on an exquisitely complex series of molecular interactions. In particular, the execution of complex biological processes requires the precise interaction and regulation of thousands of proteins. The definition of cellular interactomes by systematic analysis of protein-protein interactions has revealed complex molecular networks (39, 82, 111, 122). Most cellular proteins interact with only one or two other proteins, making only one or two connections. However, the minority of proteins interact with tens, or even hundreds, of other proteins to form network hubs. Hub proteins play key roles in regulating and orchestrating the activity of the proteins they interact with, effectively creating functional modules within the cellular interactome (35, 48, 62). The central role served by cellular hub proteins in regulating cell functions makes them ideal targets during a viral infection. By targeting a single cellular hub, a viral regulatory protein can effectively gain control over an entire module, potentially comprised of hundreds of proteins. By targeting multiple cellular hubs, a virally encoded hub can transform the architecture of the cellular protein interaction network, reprogramming virtually all aspects of cell function and behavior. The viral oncogenes of the small DNA tumor viruses encode some of the most versatile and potent viral hub proteins. Among these, adenovirus E1A is one of the best characterized and is the subject of this review.