Palmitoylation of the human cytomegalovirus tegument protein pp28 facilitates virus release

TL;DR

This study shows that a fatty modification called palmitoylation is crucial for a virus protein to help release new virus particles.

Contribution

The study identifies palmitoylation of pp28 as a novel mechanism essential for HCMV virion release and proper localization.

Findings

Palmitoylation at Cys6, Cys10, and Cys11 stabilizes pp28 and ensures its proper localization.

Disrupting palmitoylation reduces extracellular virus production without affecting intracellular replication.

Palmitoylation-deficient pp28 fails to accumulate at ERGIC-derived membranes and is degraded more rapidly.

Abstract

Tegument proteins of human cytomegalovirus (HCMV) play essential roles in viral assembly, coordinating interactions among capsids, membranes, and host-derived components. pp28 (UL99), a dominant tegument protein expressed during late infection, is essential for cytoplasmic envelopment and proper trafficking to the viral assembly compartment (vAC). Here, we identify a critical role for palmitoylation in pp28 function. Using site-directed mutagenesis and acyl-resin assisted capture (acyl-RAC) assays, we show that palmitoylation occurs at conserved cysteine residues (Cys6, Cys10, Cys11) near the N-terminus. Disruption of these residues impairs pp28 stability, alters its subcellular localization, and reduces the release of infectious virions without affecting intracellular viral replication. Confocal imaging and proteasome inhibition experiments reveal that palmitoylation-deficient pp28 is more susceptible to degradation and fails to accumulate at ERGIC-derived membranes. Consistent with these findings, recombinant HCMVs encoding pp28 mutants impaired in palmitoylation exhibit reduced extracellular viral titers. These results define palmitoylation as a key modification of pp28 that ensures proper compartmental targeting and virion maturation, underscoring a broader role for tegument lipidation in herpesvirus assembly and egress.

Human cytomegalovirus (HCMV) is a globally prevalent virus that poses a serious threat to individuals with weakened immune systems. To complete its life cycle, HCMV relies on tegument proteins, which help coordinate the assembly and release of new viral particles. In this study we show that the viral tegument protein pp28 requires palmitoylation for its stability and proper localization in infected cells. When this modification is disrupted, pp28 becomes unstable and fails to reach the compartments necessary for virus assembly, leading to a significant reduction in the production of infectious virus. Using genetic and biochemical approaches, we identified specific amino acids essential for this modification and confirmed its functional importance during infection. These findings highlight a previously underappreciated role for tegument proteins in viral egress and suggest that controlling protein lipidation could be a promising strategy to disrupt the production of infectious cytomegalovirus particles.

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