title: Domain Interaction Studies of Herpes Simplex Virus 1 Tegument Protein UL16 Reveal Its Interaction with Mitochondria.
abstract: The UL16 tegument protein of herpes simplex virus 1 (HSV-1) is conserved among all herpesviruses and plays many roles during replication. This protein has an N-terminal domain (NTD) that has been shown to bind to several viral proteins, including UL11, VP22, and glycoprotein E, and these interactions are negatively regulated by a C-terminal domain (CTD). Thus, in pairwise transfections, UL16 binding is enabled only when the CTD is absent or altered. Based on these results, we hypothesized that direct interactions occur between the NTD and the CTD. Here we report that the separated and coexpressed functional domains of UL16 are mutually responsive to each other in transfected cells and form complexes that are stable enough to be captured in coimmunoprecipitation assays. Moreover, we found that the CTD can associate with itself. To our surprise, the CTD was also found to contain a novel and intrinsic ability to localize to specific spots on mitochondria in transfected cells. Subsequent analyses of HSV-infected cells by immunogold electron microscopy and live-cell confocal imaging revealed a population of UL16 that does not merely accumulate on mitochondria but in fact makes dynamic contacts with these organelles in a time-dependent manner. These findings suggest that the domain interactions of UL16 serve to regulate not just the interaction of this tegument protein with its viral binding partners but also its interactions with mitochondria. The purpose of this novel interaction remains to be determined.
  
  
  OBJECTIVE
  The HSV-1-encoded tegument protein UL16 is involved in multiple events of the virus replication cycle, ranging from virus assembly to cell-cell spread of the virus, and hence it can serve as an important drug target. Unfortunately, a lack of both structural and functional information limits our understanding of this protein. The discovery of domain interactions within UL16 and the novel ability of UL16 to interact with mitochondria in HSV-infected cells lays a foundational framework for future investigations aimed at deciphering the structure and function of not just UL16 of HSV-1 but also its homologs in other herpesviruses.
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Pooja
authors.initials: P
authors.lastname: Chadha
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Akua
authors.initials: A
authors.lastname: Sarfo
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Microscopy Imaging Facility, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Abraham
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Jillian
authors.initials: J
authors.lastname: Carmichael
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Jun
authors.identifier: http://orcid.org/0000-0002-7104-7223
authors.initials: J
authors.lastname: Han
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA jww4@psu.edu.
authors.forename: John W
authors.initials: JW
authors.lastname: Wills
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D006561:Herpes Simplex / Q000821:virology; D018259:Herpesvirus 1, Human / Q000502:physiology*; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D063154:Mitochondrial Dynamics; D019814:Myristic Acid / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D021381:Protein Transport; D017384:Sequence Deletion; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D014764:Viral Proteins; D019814:Myristic Acid
keywords: HSV-1; UL16; domains; herpes simplex virus; mitochondria; tegument