A Tick Salivary Protein Prevents HIV-I Infection

Researchers have found that a protein isolated from the saliva of the deer tick, Ixodes scapularis, inhibits the attachment of HIV-I virus to T cells. The unraveling of this mechanism may aid in the development of future treatments for AIDS.

The tick relies on the salivary protein Salp15 to inactivate the host's T cell immune response. This is accomplished when Salp15 binds to a site on the T cell's CD4 receptor. The Salp15 binding site is located in close proximity to the site used by HIV-I gp120 glycoprotein.

Investigators at the University of Massachusetts (Amherst, USA; www.umass.edu) studied the effect of Salp15 binding on the ability of HIV-I to infect T cells. They reported in the February 2008 issue of the journal Biochemical and Biophysical Research Communications (BBRC) that Salp15 could inhibit the attachment of HIV-1 by almost 70% at the highest concentration tested. In addition to partially blocking the gp120-binding site, Salp15 prevented gp120 - CD4 interaction at least partially through its direct interaction with the virus glycoprotein. A phage-display library screen provided the interacting residues in the C1 domain of gp120.

"Salp15 binds to proteins in the CD4 receptor that are furthest from the cell membrane in both mouse and human cells,” explained senior author Dr. Juan Anguita, professor of veterinary and animal sciences at the University of Massachusetts. "This region overlaps with the binding region used by a protein on the envelope of the HIV-1 virus called gp120, making Salp15 one of several potential molecules being studied as entry-targeting inhibitors. HIV-1 patients are on powerful medications for life, and most of these have secondary effects like nerve damage and liver problems. This makes the development of new treatments an important area of research.”


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