Bovine herpesvirus 1 tegument protein <i>UL21</i> plays critical roles in viral secondary envelopment and cell-to-cell spreading

Abstract

// Farzana Shahin 1, 2 , Sohail Raza 1, 2, 6 , Kui Yang 3 , Changmin Hu 2 , Yingyu Chen 2 , Huanchun Chen 1, 2 and Aizhen Guo 1, 2, 4, 5 1 The State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China 2 College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, China 3 Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803, USA 4 Key Laboratory of Development of Veterinary Diagnostic Products, Ministry of Agriculture, Wuhan 430070, China 5 Hubei International Scientific and Technological Cooperation Base of Veterinary Epidemiology, Huazhong Agricultural University, Wuhan 430070, China 6 Department of Microbiology, University of Veterinary and Animal Sciences, Lahore 54000, Pakistan Correspondence to: Aizhen Guo, email: aizhen@mail.hzau.edu.cn Keywords: BoHV-1, interacting proteins, secondary envelopment, tegument, UL21 Received: July 13, 2017&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Accepted: September 21, 2017&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Published: October 10, 2017 ABSTRACT Bovine herpesvirus 1 (BoHV-1) UL21 is a tegument protein thought to be indispensable for efficient viral growth but its precise function in BoHV-1 is currently unknown. To determine the function of UL21 in BoHV-1 replication, we constructed a mutant virus bearing a UL21 deletion (vBoHV-1-&Delta;UL21) and its revertant virus, vBoHV-1-&Delta;UL21R, in which the UL21 gene was restored using a bacterial artificial chromosome system. The replication of vBoHV-1-&Delta;UL21 was 1,000-fold lower and its plaque size was 85% smaller than those of the wild-type virus (BoHV-1). An ultrastructural analysis showed that deletion of UL21 led to an un-enveloped capsid accumulation in the cytoplasm, whereas nucleocapsid egress was not impaired, suggesting that UL21 is critical for secondary envelopment in BoHV-1. Co-immunoprecipitation assays revealed that HA-tagged UL21 pulled down UL16 , suggesting that these two proteins form a complex, and this was further confirmed by a co-immunofluorescence assay. Taken together, these data provide evidence that UL21 plays critical roles in BoHV-1 secondary envelopment, and UL16 is likely to be involved in these activities.