The human immunodeficiency virus (HIV) encodes vif, a virulence factor that deactivates the enzyme APOBEC-3G. This enzyme may be the key to the body's natural defense against HIV. A new study published in Nature discerning the crystal structure of the enzyme may be one of the first to show the potential of blocking vif and allowing APOBEC-3G to attack HIV in the fight against the ongoing epidemic of AIDS. The enzyme blocks HIV replication and, if vif is prevented from acting, the enzyme will continue to prevent HIV from causing AIDS. Knowing the structure of the enzyme will aid the development of drugs that prevent vif from binding.