WASHINGTON — A drug being tested for treatment of the common cold possibly could be modified to become effective against SARS (news - web sites), according to a new study.

Virus researchers in Germany report that they have developed a model for the crystalline structure of a key protein used by the SARS virus to infect cells, an important step toward finding a drug that would combat the deadly pathogen.

In a study appearing this week in the journal Science, the researchers say their study suggests an experimental common cold drug called AG7088 may be able to keep the SARS virus from replicating.

AG7088 is in clinical trials for the treatment of rhinovirus, a pathogen that can cause the common cold, according to experts at the journal Science.

Dr. Tony Fauci, head of the Institute for Allergy and Infectious Diseases, said the SARS study is important because it develops a model of a protein that could become a key target for an anti-viral drug and because the researchers have identified a compound already developed to treat a similar virus.

"This is a cogent example of progress" against SARS, said Fauci, but he cautioned that much work remains to be done to prove that the laboratory findings can be converted to medication that would treat patients.

A number of anti-viral drugs are being evaluated in government laboratories to determine if they might be effective against SARS, or severe acute respiratory syndrome. There currently are no drugs to treat the disease.

SARS is a highly contagious virus that can be spread by either sneezing or coughing, or even through contact with surfaces recently contaminated by the virus. More than 7,400 SARS cases have been reported worldwide, and the international death toll has reached at least 580.

In the study, senior author Rolf Hilgenfeld of the University of Luebeck in Germany said he and his co-workers developed a model for the crystalline shape of an enzyme that the SARS virus uses to infect cells. Based on this model, Hilgenfeld said in a statement that AG7088 provides "a good starting point" for developing a drug that would block the action of the enzyme and, thus, prevent SARS from reproducing within a cell.

The enzyme, called a protease, is typical of proteins viruses use to take over a host cell and force that cell to make new virus particles. Blocking the protease action would not prevent an initial infection, experts say, but it would prevent spread of the virus through the body.

Hilgenfeld said the researchers found close similarities between the protease enzyme of rhinovirus and the protein in SARS, which is a type of coronavirus.

Since AG7088 is effective against rhinovirus, he said, then a modified version of the drug might inhibit the action of the SARS virus enzyme.