Stevens, A. W. | bioRxiv Science

bioRxiv2024

Structure-Guided Mutagenesis Targeting Interactions between pp150 Tegument Protein and Small Capsid Protein Identify Five Lethal and Two Live Attenuated HCMV Mutants

Human cytomegalovirus (HCMV) replication relies on a nucleocapsid coat of the 150kDa, subfamily-specific tegument phosphoprotein (pp150) to regulate cytoplasmic virion maturation. While recent structural studies revealed pp150-capsid interactions, the role of specific amino-acids involved in these interactions have not been established experimentally. In this study, pp150 and the small capsid protein (SCP), one of pp150s binding partners found atop the major capsid protein (MCP), were subjected to mutational and structural analyses. Mutations to clusters of polar or hydrophobic residues along the pp150-SCP interface abolished viral replication, with no replication detected in mutant virus-infected cells. Notably, a single point mutation at the pp150-MCP interface significantly attenuated viral replication, unlike the situation of pp150-deletion mutation where capsids degraded outside host nuclei. These functionally significant mutations targeting pp150-capsid interactions, particularly the pp150 K255E replication-attenuated mutant, can be explored to overcome the historical challenges of developing effective antivirals and vaccines against HCMV infection.

microbiology↗

bioRxiv2022

Asymmetric Reconstruction of the Aquareovirus Core at Near-Atomic Resolution and Mechanism of Transcriptional Initiation

The Reoviridae family of dsRNA viruses is characterized by its members capacity for endogenous transcription of their multipartite genomes within proteinaceous capsids of 1 to 3 layers. These viruses share inner core particles (ICPs) that conform to icosahedral, T=2*, symmetry, but differ in two major respects: first, the presence or absence of RNA-capping turrets at each icosahedral vertex; second, the number of additional host-specific capsid layers that are often lost upon cell entry. While the role of these additional layers in host infection is generally understood, the absence of asymmetric ICP structures from turreted, multilayered reoviruses has obfuscated our understanding of how successive removal of these external layers impact the structural organization of the ICP and transcription initiation. Here, we present the 3.3 [A] resolution structure of the aquareovirus (ARV) ICP, and atomic models of the capsid proteins VP3 and VP6, transcriptional enzymatic complex (TEC) subunits VP2 and VP4, and RNA-capping turret protein VP1. These structures reveal significant differences when compared to those of the coated ARV, as well as their counterparts in single-layered cytoplasmic polyhedrosis virus (CPV). Compared to the double-layered ARV virion and infectious subvirion particle structures, the ARV ICP undergoes significant capsid expansion and widening of the nucleotide processing channels in its TEC and turret. Thus, the loss of outer capsid layers may regulate transcription initiation in ARV, unlike CPV which relies solely on allosteric regulation by binding transcriptional cofactors. These results shed new light on the mechanism of transcription initiation amongst turreted, multilayered members of Reoviridae.

molecular biology↗