A recent study by Harvard Medical School researchers may offer new insight into the methods with which viruses enter cells and cause disease.

The study, headed by James M. Cunningham, assistant professor of medicine at the Medical School, reported that the viral receptor, a host protein which viruses use to enter the cell, has a molecular structure and cellular function vastly different than those previously described.

Investigators studied the mechanism by which a mouse leukemia virus, MuLV, enters cells. They found that the receptor for this virus is a channel that allows positively charged amino acids to enter the cell. In further study, he and colleagues found that the gene encoding the sequence for this receptor was one whose structure allows specific molecules to pass through it.

Computer-assisted searches comparing the receptor's amino acid sequence to other known proteins found that they were slightly similar to two amino acid importing proteins of yeast. Experiments with frog eggs proved that the protein did in fact play a role similar to that of these previously discovered proteins.

The group is currently studying two inherited diseases in humans, lysinuric protein intolerance (LPI) and cystinuria. Both diseases affect the ability of cells to import certain amino acids. Researchers believe that LPI, which creates a toxicity for proteins containing a certain amino acid, lysine, may be caused by a mutation in the protein under study.