title: The herpes simplex virus 1 UL17 protein is the second constituent of the capsid vertex-specific component required for DNA packaging and retention.
abstract: The herpes simplex virus (HSV) UL17 and UL25 minor capsid proteins are essential for DNA packaging. They are thought to comprise a molecule arrayed in five copies around each of the capsid vertices. This molecule was initially termed the "C-capsid-specific component" (CCSC) (B. L. Trus et al., Mol. Cell 26:479-489, 2007), but as we have subsequently observed this feature on reconstructions of A, B, and C capsids, we now refer to it more generally as the "capsid vertex-specific component" (CVSC) (S. K. Cockrell et al., J. Virol. 85:4875-4887, 2011). We previously confirmed that UL25 occupies the vertex-distal region of the CVSC density by visualizing a large UL25-specific tag in reconstructions calculated from cryo-electron microscopy (cryo-EM) images. We have pursued the same strategy to determine the capsid location of the UL17 protein. Recombinant viruses were generated that contained either a small tandem affinity purification (TAP) tag or the green fluorescent protein (GFP) attached to the C terminus of UL17. Purification of the TAP-tagged UL17 or a similarly TAP-tagged UL25 protein clearly demonstrated that the two proteins interact. A cryo-EM reconstruction of capsids containing the UL17-GFP protein reveals that UL17 is the second component of the CVSC and suggests that UL17 interfaces with the other CVSC component, UL25, through its C terminus. The portion of UL17 nearest the vertex appears to be poorly constrained, which may provide flexibility in interacting with tegument proteins or the DNA-packaging machinery at the portal vertex. The exposed locations of the UL17 and UL25 proteins on the HSV-1 capsid exterior suggest that they may be attractive targets for highly specific antivirals.
authors.affiliation: Department of Structural Biology, University of Pittsburgh, Biomedical Science Tower 3, 3501 5th Ave., Pittsburgh, PA 15260, USA.
authors.forename: Katerina
authors.initials: K
authors.lastname: Toropova
authors.forename: Jamie B
authors.initials: JB
authors.lastname: Huffman
authors.forename: Fred L
authors.initials: FL
authors.lastname: Homa
authors.forename: James F
authors.initials: JF
authors.lastname: Conway
mesh_terms: D000818:Animals; D001483:Base Sequence; D002213:Capsid; D002522:Chlorocebus aethiops; D002846:Chromatography, Affinity; D020285:Cryoelectron Microscopy; D042003:DNA Packaging; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D049452:Green Fluorescent Proteins / Q000235:genetics; D014709:Vero Cells; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D014764:Viral Proteins; C069185:DNA cleavage and packaging proteins, Herpesvirus; D049452:Green Fluorescent Proteins