Synaptic vesicle-like lipidome of human cytomegalovirus virions reveals a role for SNARE machinery in virion egress

Abstract

Human cytomegalovirus induces and requires fatty acid synthesis. This suggests an essential role for lipidome remodeling in viral replication. We used mass spectrometry to quantify glycerophospholipids in mock-infected and virus-infected fibroblasts, as well as in virions. Although the lipid composition of mock-infected and virus-infected fibroblasts was similar, virions were markedly different. The virion envelope contained twofold more phosphatidylethanolamines and threefold less phosphatidylserines than the host cell. This indicates that the virus buds from a membrane with a different lipid composition from the host cell as a whole. Compared with published datasets, the virion envelope showed the greatest similarity to the synaptic vesicle lipidome. Synaptosomeassociated protein of 25 kDa (SNAP-25) is a component of the complex that mediates exocytosis of synaptic vesicles in neurons; and its homolog, SNAP-23, functions in exocytosis in many other cell types. Infection induced the relocation of SNAP-23 to the cytoplasmic viral assembly zone, and knockdown of SNAP-23 inhibited the production of virus. We propose that cytomegalovirus capsids acquire their envelope by budding into vesicles with a lipid composition similar to that of synaptic vesicles, which subsequently fuse with the plasma membrane to release virions from the cell.H uman cytomegalovirus (HCMV) is a member of the enveloped herpesvirus family. It is a widespread pathogen that can cause disease in immunologically immature or compromised individuals (1). HCMV infection substantially alters the metabolism of cultured fibroblasts (2), inducing a marked increase in the flux of carbon from glucose into fatty acids (3). Consistent with the enhanced flux, inhibition of acetyl-CoA carboxylase, the first committed enzyme in the fatty acid biosynthetic pathway, reduces the yield of infectious virus. Thus, lipid synthesis is required during the HCMV replication cycle. Newly synthesized membranes likely accumulate in the assembly compartment (4-8), a virus-induced organelle with virus-coded proteins and cellular proteins that include markers of the exocytic and endocytic networks. This is the site at which viral capsids acquire an envelope (9-12).Glycerophospholipids are major components of cellular membranes. This family of lipids consists of a glycerol backbone, a functional head group, and two fatty acids of varying length and unsaturation. Phosphatidic acid (PA) serves as the basic glycerophospholipid building block, with its phosphate group esterified to a head group to produce phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylglycerol (PG), or diphosphatidylglycerol. By using mass spectrometry, it is possible to identify and quantify numerous glycerolphospholipid species, differing in head group, acyl chain length, and degree of unsaturation (13-16). This quantitative lipidomics approach has been used to generate detailed descriptions of several viral envelopes, including those acqui...

Human kinome profiling identifies a requirement for AMP-activated protein kinase during human cytomegalovirus infection

“…The effects of compound C were profound, with most of the metabolome changes due to HCMV reversed in the presence of compound C. One exception involved cytidine diphosphate (CDP)- ethanolamine and CDP-choline, which are used in the Kennedy pathway of phosphatidylcholine and phosphatidylethanolamine synthesis and remained elevated in the HCMV-infected, compound C-treated cells. Phosphatidylethanolamines are strongly enriched in HCMV virions (30). Another involved N-acetylated amino acids (e.g., acetylaspartate, acetylglutamate, and acetylalanine).…”

Phospholipase D Facilitates Efficient Entry of Influenza Virus, Allowing Escape from Innate Immune Inhibition

“…The lower organic layer was isolated, synthetic odd-carbon phospholipids (four per phospholipid class) were added as standards, and the solvent was evaporated. The resulting lipid film was dissolved in 100 l of 58:40:2 isopropanol, hexane, 100 mM NH 4 COOH (aqueous) (mobile phase A) (16). Samples containing n-butyl alcohol were extracted similarly, and 5 l of 10 g/ml 32:0 phosphatidylmethanol was added as an internal standard.…”

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