Technologies for Proteome-Wide Discovery of Extracellular Host-Pathogen Interactions

Martinez-Martin, Nadia

Receptor Discovery. Recently, we applied this ePPI discovery platform to the study of extracellular viral proteins ( Figure 1 ), with a focus on human adenovirus-(HAdV-) encoded immunomodulatory proteins [28] . Despite the increasing relevance of HAdV as both pathogens and therapeutic vectors, information on the interaction of these viruses with the host immune system remains scarce [73, 74] . Interestingly, the immunomodulatory proteins encoded by these viruses, termed E3 proteins, show substantial diversity in their ECDs across and within viral species and constitute one of the most divergent regions of the HAdV genome [75, 76] . Given this striking variability, the E3 proteins have been suggested to play a role in viral tropism and pathogenesis, yet the functions of virtually all E3 proteins have remained unknown [73] . In our study, we took advantage of such unique variability to evaluate the effect of viral immunomodulatory protein diversity in extracellular host targeting. Screening of a substantial number of E3 proteins encoded by different HAdV species using the extracellular protein microarray platform allowed identification of over 50 novel virus-host interactions encompassing 5 viral species, which were fully validated by orthogonal methods [28] . These findings revealed significant diversity in extracellular host targeting and, moreover, allowed identification of semiconserved host targets, pointing towards specific human receptors that may represent previously unrecognized hubs for viral perturbation. Furthermore, most of the E3 immunomodulators were identified as multifunctional proteins, suggesting that viruses have evolved proteins capable of interfering with several cellular functions, a strategy consistent with the optimization of limited genomic resources. Such economic targeting has been often observed in intracellular targeting [15] [16] [17] , but so far few examples of widespread targeting in the extracellular environment have been reported [28, [77] [78] [79] [80] , let alone a global elucidation of ePPI networks, in part due to the technical challenges associated with ePPI detection.