Comprehensive genetic dissection of poxvirus membrane assembly and function

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The zoonotic potential of members of the genus Orthopoxvirus (orthopoxviruses) of mammal- infecting poxviruses represent a continued threat to global public health. A hallmark of the complex biology of orthopoxvirus multiplication in the host cell cytoplasm is the generation of two distinct infectious forms—intracellular mature virions (IMV), which remain largely cell- associated, and enveloped virions (EV), which are critical for extracellular viral spread. EVs bear a unique complement of eight virus-encoded membrane proteins at their surface that influence tissue tropism, long-range in vivo dissemination, and ultimately, virulence; provide key targets for vaccine-induced and therapeutic antibodies; and are important determinants of the therapeutic potential of oncolytic poxvirus vectors. Despite their importance, a comprehensive understanding of EVs is challenged by the complex networks of virus-host and virus-virus interactions that underlie their morphogenesis and function. Our overall objective is to unravel these functional protein interaction networks through a combination of genetic and proteomic approaches. Using a new platform for unbiased and deep mutagenesis of any genomic locus in the prototypic orthopoxvirus, vaccinia virus (VACV), we conducted deep-mutational scans (DMS) of two EV proteins, A33 and A34, in the context of infectious viral particles and identified novel regiospecific mutations that enhance EV fitness. We will elucidate the mechanisms of action of these mutants. In parallel, we will perform genetic modifier and proteomic screens to uncover new functional interactions of A33/A34 with viral and host proteins. Collectively, these studies will provide new information on how EVs—critical for both the virulence of orthopoxviruses and their utility as oncolytic vectors—assemble, egress, and spread to new cells during infection.