Intracellular targeting signals contribute to localization of coronavirus spike proteins near the virus assembly site.
Coronavirus budding at the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) requires accumulation of the viral envelope proteins at this point in the secretory pathway. Here we demonstrate that the spike (S) protein from the group 3 coronavirus infectious bronchitis virus (IBV) contains a canonical dilysine endoplasmic reticulum retrieval signal (-KKXX-COOH) in its cytoplasmic tail. This signal can retain a chimeric reporter protein in the ERGIC and when mutated allows transport of the full-length S protein as well as the chimera to the plasma membrane. Interestingly, the IBV S protein also contains a tyrosine-based endocytosis signal in its cytoplasmic tail, suggesting that any S protein that escapes the ERGIC will be rapidly endocytosed when it reaches the plasma membrane. We also identified a novel dibasic motif (-KXHXX-COOH) in the cytoplasmic tails of S proteins from group 1 coronaviruses and from the newly identified coronavirus implicated in severe acute respiratory syndrome. This dibasic motif also retained a reporter protein in the ERGIC, similar to the dilysine motif in IBV S. The cytoplasmic tails of S proteins from group 2 coronaviruses lack an intracellular localization signal. The inherent differences in S-protein trafficking could point to interesting variations in pathogenesis of coronaviruses, since increased levels of surface S protein could promote syncytium formation and direct cell-to-cell spread of the infection.
Lontok
Erik
E
Department of Cell Biology, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA.
Corse
Emily
E
Machamer
Carolyn E
CE
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D004151:Dipeptides; D004721:Endoplasmic Reticulum / Q000502:physiology*; D006056:Golgi Apparatus / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D001351:Infectious bronchitis virus / Q000502:physiology; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D021381:Protein Transport; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000502:physiology*; D019065:Virus Assembly
D004151:Dipeptides; D008562:Membrane Glycoproteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus; C024575:lysyllysine