| The novel human pathogen Severe Acute Respiratory Syndrome Coronavirus, SARS-CoV, emerged in 2002 in China. SARS-CoV caused severe respiratory disease with a 10% mortality rate in infected patients. Unlike many other enveloped viruses, SARS-CoV assembles and buds intracellularly at the endoplasmic reticulum Golgi intermediate compartment (ERGIC). For the production of infectious virus, the SARS-CoV envelope proteins are targeted to the virus assembly site for assembly and budding. SARS-CoV encodes three envelope proteins: spike, membrane and envelope. The SARS-CoV spike (S) glycoprotein is necessary for the production of infectious virus, although it is dispensable for virus assembly. S binds angiotensin converting enzyme 2, the receptor for SARS-CoV, causing virus-cell and cell-cell fusion.;The work described here demonstrates that the SARS-CoV S protein contains a non-canonical endoplasmic retrieval (ER) signal that binds COPI, the coat protein that recycles escaped cargo to the ER. Addition of the dibasic ER retrieval signal, K(Lys)H(His)xx-COOH, slowed the maturation of reporter proteins through the secretory pathway. Although the dibasic ER retrieval signal did not prevent trafficking of the S protein to the plasma membrane, it was necessary for facilitating efficient S and membrane (M) protein interaction, presumably via S protein recycling. Thus, the S protein was localized to the virus assembly site through its interaction with membrane protein. The S-M interaction was mediated by the M protein cytoplasmic tail. A tyrosine residue, Y195, in the SARS-CoV M protein cytoplasmic tail was necessary for efficient S-M protein interaction in vitro. When Y195 was mutated, M protein could no longer retain S protein in the Golgi region, reduce S protein trafficking through the secretory pathway or reduce the amount of S protein at the plasma membrane. Palmitoylation of the spike protein cytoplasmic tail was not necessary for S-M interaction, but was necessary for S partitioning into detergent resistant membranes and for cell-cell fusion.;The S protein is the major antigenic protein and many SARS-CoV S protein antibodies can neutralize infection. Understanding the intracellular trafficking of the SARS-CoV S protein is important for designing therapeutic agents to treat SARS-CoV or other novel coronavirus pathogens that may emerge in the future. |
