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[BEIJING] A study has revealed the most likely route by which the SARS virus  enters host cells, paving the way for future drug development that blocks viral invasion.

Before abating in mid-2003, SARS (Severe Acute Respiratory Syndrome) killed 774 people, and infected more than 8,000 globally. However, many features of the deadly virus — such as how it infects host cells — have not been well defined.

Researchers had previously found that the SARS virus enters cells through 'membrane fusion', where the virus binds to receptors on the host cell surface and then transports its genomes into host cells.

Other research has suggested that the virus uses 'endocytosis', a process whereby the cell membrane folds inwards and engulfs substances in order to take them in.

In their study, published yesterday (29 January) in Cell Research, Jiang Chengyu and colleagues from the Beijing-based Peking Union Medical College found the specific type of endocytic pathway that the virus uses.

In the study, scientists monitored the movement of the receptor that recognises SARS, from the cell membrane to inside the cell. They then used different drugs to block the functions of known cell entry pathways to determine which route the virus took.

"While some studies have shown the possible endocytic pathway for SARS, we have revealed this is a concrete route of entry," Jiang told SciDev.Net.

By doing so, the research team identified that the SARS virus does not rely on the conventional endocytic pathways to enter cells. Rather, 'lipid rafts', a section of the cell membrane that is enriched with cholesterol, play an active role in the entry of the SARS virus.

"In future studies, the rafts could be a potential target for treating SARS by blocking virus entry into cells," says Jiang.

Liao Kan, a senior scientist from the Shanghai Institutes for Biological Sciences at the Chinese Academy of Sciences, praises the study as significant because it has revealed a viral entry pathway, which so far, has been poorly understood.

"But further studies are needed to reveal whether this is the only route the SARS virus uses to enter cells," Liao told SciDev.Net. "If the virus has two gates to enter, when you close one door with potential drugs, the virus may take the other way."

Reference: Cell Research, doi 10.1038/cr.2008.15 (2008)

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