A novel sorting signal for intracellular localization is present in the S protein of a porcine coronavirus but absent from severe acute respiratory syndrome-associated coronavirus.
Coronaviruses (CoV) mature by a budding process at intracellular membranes. Here we showed that the major surface protein S of a porcine CoV (transmissible gastroenteritis virus) is not transported to the cell surface but is retained intracellularly. Site-directed mutagenesis indicated that a tyrosine-dependent signal (YXXI) in the cytoplasmic tail is essential for intracellular localization of the S protein. Surface expression of mutant proteins was evident by immunofluorescence analysis and surface biotinylation. Intracellularly retained S proteins only contained endoglycosidase H-sensitive N-glycans, whereas mutant proteins that migrated to the plasma membrane acquired N-linked oligosaccharides of the complex type. Corresponding tyrosine residues are present in the cytoplasmic tails of the S proteins of other animal CoV but not in the tail portion of the S protein of severe acute respiratory syndrome (SARS)-CoV. Changing the SEPV tetrapeptide in the cytoplasmic tail to YEPI resulted in intracellular retention of the S protein of SARS-CoV. As the S proteins of CoV have receptor binding and fusion activities and are the main target of neutralizing antibodies, the differences in the transport behavior of the S proteins suggest different strategies in the virus host interactions between SARS-CoV and other coronaviruses.
Institut für Virologie, Tierärztliche Hochschule Hannover, Bünteweg 17, D-30559, Germany.
Christel
C
Schwegmann-Wessels
Marwan
M
Al-Falah
David
D
Escors
Zai
Z
Wang
Gert
G
Zimmer
Hongkui
H
Deng
Luis
L
Enjuanes
Hassan Y
HY
Naim
Georg
G
Herrler
D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D017934:Coronavirus / Q000145:classification / Q000502:physiology*; D017931:DNA Primers; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012128:Respiratory Distress Syndrome / Q000821:virology*; D064370:Spike Glycoprotein, Coronavirus; D013552:Swine; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D008562:Membrane Glycoproteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus