Identification of Viral and Cellular Proteins in Proximity to the HSV-2 pUL16 Tegument Protein in Infected Cells

Orthologs of the herpes simplex virus (HSV) pUL16 tegument protein are conserved throughout the Orthoherpesviridae family. During HSV infection, pUL16 functions in the nuclear egress of nascent nucleocapsids from the nucleus to the cytoplasm, prevents the docking of nascent cytoplasmic nucleocapsids to nuclear pore complexes, promotes the final envelopment of cytoplasmic nucleocapsids, and enhances cell-to-cell spread of virus infection. How pUL16 performs these diverse functions is poorly understood. To gain further insight into the mechanisms by which pUL16 mediates its activities, we utilized a BioID approach to identify cellular and viral proteins in proximity to pUL16 during the infection of human keratinocytes. By comparing proteins in proximity to pUL16 during infection with proteins in proximity to its well-known virus-encoded binding partner, pUL21, we provide new insight into the activities of pUL16 that likely occur in complex with pUL21 and those that are independent of pUL21. A key function of pUL21 is to deliver protein phosphatase 1 (PP1) to viral and cellular substrates to mediate their dephosphorylation. Intriguingly, the findings presented suggest that pUL16 interactions with pUL21 may regulate the isoform of PP1 that is bound to pUL21 and thereby regulate the specificity of substrate dephosphorylation. ImportanceHSV-1 and HSV-2 are important human pathogens that currently infect roughly 3.8 billion and 520 million people, respectively. These viruses cause lifelong, recurrent, infections and cause a variety of diseases including vesicular lesions of the oral and genital mucosa, corneal blindness, meningitis, encephalitis and devastating neonatal infections. The HSV pUL16 tegument protein performs a number of critical functions for the virus that influence virion assembly and the spread of infection between cells. In this study we have identified cellular and viral proteins that are proximal to pUL16 during infection of human keratinocytes, providing new insight into the mechanisms used by pUL16 to perform its activities.