Abstract
In all herpesviruses, the space between the capsid shell and the lipid envelope is occupied by the unique tegument layer composed of proteins that, in addition to structural roles, play many other roles in the viral replication. UL37 is a highly conserved tegument protein that has activities ranging from virion morphogenesis to directional capsid trafficking to manipulation of the host innate immune response and binds multiple partners. The N-terminal half of UL37 (UL37N) has a compact bean-shaped α-helical structure that contains a surface region essential for neuroinvasion. However, no biochemical or structural information is currently available for the C-terminal half of UL37 (UL37C) that mediates most of its interactions with multiple binding partners. Here, we show that the C-terminal half of UL37 from pseudorabies virus UL37C is a conformationally flexible monomer composed of an elongated folded core and an unstructured C-terminal tail. This elongated structure, along with that of its binding partner UL36, explains the nature of filamentous tegument structures bridging the capsid and the envelope. We propose that the dynamic nature of UL37 underlies its ability to perform diverse roles during viral replication.
Highlights
In all herpesviruses, the space between the capsid shell and the lipid envelope is occupied by the unique tegument layer composed of proteins that, in addition to structural roles, play many other roles in the viral replication
SAXS profiles were obtained for three constructs of PRV UL37C and for HSV-1 UL37N, a compact, conformationally rigid protein that served as a control (Fig. 4 and Fig. 5A)
In HSV-1 alone, UL37 interacts with viral proteins UL36 [34] and gK [3] and host proteins dystonin [23], TNF receptor–associated factor 6 (TRAF6) [25], and retinoic acid-inducible gene I (RIG-I) [26]
Summary
The space between the capsid shell and the lipid envelope is occupied by the unique tegument layer composed of proteins that, in addition to structural roles, play many other roles in the viral replication. UL37 is a highly conserved tegument protein that has activities ranging from virion morphogenesis to directional capsid trafficking to manipulation of the host innate immune response and binds multiple partners. We show that the C-terminal half of UL37 from pseudorabies virus UL37C is a conformationally flexible monomer composed of an elongated folded core and an unstructured C-terminal tail This elongated structure, along with that of its binding partner UL36, explains the nature of filamentous tegument structures bridging the capsid and the envelope. In addition to providing a large surface with many potential binding sites for its multiple binding partners, UL37C can adopt several distinct conformations, each of which mediates a specific subset of UL37 activities We propose that this conformational flexibility contributes to the multifunctionality of UL37
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