Xiaojiang Chen, the study leader, describes this enzyme as an enzyme known as APOBEC-3G, which is present in every human cell.
He says that this enzyme is capable of stopping HIV at the first step of replication, when the retrovirus transcribes its RNA into viral DNA.
The researcher adds that the discovery sheds light on how and where the enzyme binds to the viral DNA, mutating and destroying it.
"We understand how this enzyme can interact with DNA. This understanding provides a platform for designing anti-HIV drugs," Nature magazine quoted Chen, a professor of molecular and computational biology at USC, as saying.
According to the researchers, the HIV virus has evolved to encode the protein Vif, known as a "virulence factor", that blocks APOBEC-3G.
When the enzyme gets deactivated, the RNA of the HIV virus can be successfully transcribed to viral DNA, an essential step for infection and for producing many more HIV viruses.
Chen insists that his team's findings provide significant clues as to where Vif binds to APOBEC-3G, something that may pave the way for drugs to prevent the deactivation of the enzyme.
"We were born with it, and it's there waiting," he said.
Besides fighting HIV, he added, APOBEC-3G could also inhibit the Hepatitis B virus.
Other members of the APOBEC family serve important roles in antibody maturation, fat metabolism and heart development.
Mapping the structure of APOBEC-3G at the atomic level is a goal that "has been sought after worldwide because of its significance," Chen said.