Palmitoylations on murine coronavirus spike proteins are essential for virion assembly and infectivity.
Coronavirus spike (S) proteins are palmitoylated at several cysteine residues clustered near their transmembrane-spanning domains. This is achieved by cellular palmitoyl acyltransferases (PATs), which can modify newly synthesized S proteins before they are assembled into virion envelopes at the intermediate compartment of the exocytic pathway. To address the importance of these fatty acylations to coronavirus infection, we exposed infected cells to 2-bromopalmitate (2-BP), a specific PAT inhibitor. 2-BP profoundly reduced the specific infectivities of murine coronaviruses at very low, nontoxic doses that were inert to alphavirus and rhabdovirus infections. 2-BP effected only two- to fivefold reductions in S palmitoylation, yet this correlated with reduced S complexing with virion membrane (M) proteins and consequent exclusion of S from virions. At defined 2-BP doses, underpalmitoylated S proteins instead trafficked to infected cell surfaces and elicited cell-cell membrane fusions, suggesting that the acyl chain adducts are more critical to virion assembly than to S-induced syncytial developments. These studies involving pharmacologic inhibition of S protein palmitoylation were complemented with molecular genetic analyses in which cysteine acylation substrates were mutated. Notably, some mutations (C1347F and C1348S) did not interfere with S incorporation into virions, indicating that only a subset of the cysteine-rich region provides the essential S-assembly functions. However, the C1347F/C1348S mutant viruses exhibited relatively low specific infectivities, similar to virions secreted from 2-BP-treated cultures. Our collective results indicate that the palmitate adducts on coronavirus S proteins are necessary in assembly and also in positioning the assembled envelope proteins for maximal infectivity.
Thorp
Edward B
EB
Department of Microbiology and Immunology, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153, USA.
Boscarino
Joseph A
JA
Logan
Hillary L
HL
Goletz
Jeffrey T
JT
Gallagher
Thomas M
TM
D000215:Acylation; D000217:Acyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000502:physiology*; D051379:Mice; D006517:Murine hepatitis virus / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*; D010168:Palmitates / Q000494:pharmacology; D010169:Palmitic Acids / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D011995:Recombination, Genetic; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000502:physiology*; D014763:Viral Matrix Proteins / Q000502:physiology; D014774:Virulence / Q000187:drug effects; D019065:Virus Assembly
D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D010168:Palmitates; D010169:Palmitic Acids; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; D014763:Viral Matrix Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus; C022776:2-bromopalmitate; D000217:Acyltransferases