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Differential maturation and subcellular localization of severe acute respiratory syndrome coronavirus surface proteins S, M and E

Béatrice Nal^1,

Cheman Chan^1,

¹ HKU-Pasteur Research Centre, 8 Sassoon Road, Hong Kong, China
² Unité d'Immunologie Virale, Institut Pasteur, 25 rue du Dr Roux, Paris, France
³ Unité de Génétique Moléculaire des Virus Respiratoires, Institut Pasteur, 25 rue du Dr Roux, Paris, France
⁴ Department of Microbiology, The University of Hong Kong, Hong Kong, China

Correspondence
Béatrice Nal
bnal{at}hkucc.hku.hk

Post-translational modifications and correct subcellular localization of viral structural proteins are prerequisites for assembly and budding of enveloped viruses. Coronaviruses, like the severe acute respiratory syndrome-associated virus (SARS-CoV), bud from the endoplasmic reticulum-Golgi intermediate compartment. In this study, the subcellular distribution and maturation of SARS-CoV surface proteins S, M and E were analysed by using C-terminally tagged proteins. As early as 30 min post-entry into the endoplasmic reticulum, high-mannosylated S assembles into trimers prior to acquisition of complex N-glycans in the Golgi. Like S, M acquires high-mannose N-glycans that are subsequently modified into complex N-glycans in the Golgi. The N-glycosylation profile and the absence of O-glycosylation on M protein relate SARS-CoV to the previously described group 1 and 3 coronaviruses. Immunofluorescence analysis shows that S is detected in several compartments along the secretory pathway from the endoplasmic reticulum to the plasma membrane while M predominantly localizes in the Golgi, where it accumulates, and in trafficking vesicles. The E protein is not glycosylated. Pulse-chase labelling and confocal microscopy in the presence of protein translation inhibitor cycloheximide revealed that the E protein has a short half-life of 30 min. E protein is found in bright perinuclear patches colocalizing with endoplasmic reticulum markers. In conclusion, SARS-CoV surface proteins S, M and E show differential subcellular localizations when expressed alone suggesting that additional cellular or viral factors might be required for coordinated trafficking to the virus assembly site in the endoplasmic reticulum-Golgi intermediate compartment.

Supplementary material available in JGV Online.

These authors contributed equally to this work.

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