Examining the role of UL36p in HSV-1 microtubule dependent motility

Abstract

Microtubule mediated transport is essential for egress of Herpes Simplex Virus 1 (HSV-1), yet there is currently little known regarding the mechanism that drives this movement. In addition, there are no known proteins, cellular or viral, that have been identified as being essential for the motility of HSV-1. However, a viral gene UL36, which encodes a 3,164 amino acid protein that binds directly to the capsid and is believed to be the first layer of tegument, a dense proteinaceous layer found between the capsid and envelope, has been implicated in this process.;We have previously shown that we are able to reproduce HSV-1 trafficking on microtubules using an in vitro system that consists of a microchamber containing rhodamine labeled microtubules, a GFP-fluorescing virus, and ATP. In order to test whether UL36p is required for microtubule-mediated motility, we utilized a UL36p null virus, KDeltaUL36GFP, which contains a large deletion in the UL36 gene and GFP fused to a capsid protein.;Here we report that the large tegument protein UL36p is essential for microtubule mediated trafficking. A membrane-associated population of KDeltaUL36GFP displayed a slightly decreased binding to microtubules in our microchamber assay and a two-thirds decrease in motility, which was restored when UL36p was supplied in trans by a complementing cell line. Although these viral particles contained normal amounts of tegument proteins VP16, vhs, and VP22, they displayed a 3 log decrease in infectivity and showed a different morphology compared to wild type.;Because KDeltaUL36GFP is still able to produce the amino terminal 400 amino acids of UL36p, which may still be biologically active, we next used HSV-1 strain GSDeltaUL36 which contains a full UL36p deletion. Motility was not restored when UL36p was supplied in trans, however, this may be attributed to decreased amounts of UL36p expressed in the complementing cell line. Further characterization of this motility showed that it was not sensitive to kinesin and dynein inhibitors. Loss of this protein also resulted in slight mislocalization of HSV-1 capsids within the cell.