United Press International - October 14, 2008

LOS ANGELES, Oct. 14 (UPI) -- U.S. medical scientists say they've determined the atomic structure of a key enzyme involved in inhibiting the human immunodeficiency virus.

The researchers, led by Professor Xiaojiang Chen of the University of Southern California, said the enzyme APOBEC-3G -- present in every human cell -- is capable of stopping HIV at the first step of replication, when the retrovirus transcribes its RNA into viral DNA.

The reason APOBEC-3G works so well, but people still develop AIDS, is because the HIV virus has evolved to encode the protein Vif, which blocks APOBEC-3G. But Chen said his group's research offers important clues on where Vif binds to APOBEC-3G.

Those findings, he said, could be used to design drugs that would prevent Vif from binding, allowing APOBEC-3G to do its job. That, he added, would unlock humans' innate ability to fight HIV.

The study that included Lauren Holden, Courtney Prochnow, Y. Paul Chang, Ronda Bransteitter, Linda Chelico, Udayaditya Sen and Professors Raymond Stevens and Myron Goodman appears in the online edition of the journal Nature.

On the Net: Nature

Reference: Crystal structure of the anti-viral APOBEC3G catalytic domain and functional implications. Nature. 2008 Oct 12. [Epub ahead of print]

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