APOBEC3

APOBEC3 is a family of enzymes belonging to the apolipoprotein B mRNA editing catalytic polypeptide-like (APOBEC) family of proteins. These proteins are characterized by their cytidine deaminase activity, meaning they can deaminate cytosine bases in DNA and RNA. In humans, there are seven functional APOBEC3 genes, APOBEC3A through APOBEC3H.

The primary known function of APOBEC3 proteins is antiviral defense. They are expressed in various cell types, particularly those involved in immune responses. When a virus, such as HIV, infects a cell, APOBEC3 enzymes can be incorporated into viral particles. Once the virus replicates, APOBEC3 enzymes can deaminate cytosine bases in the viral DNA. This deamination leads to G-to-A mutations in the viral genome, which often renders the virus non-infectious or contributes to its degradation.

Different APOBEC3 proteins have varying substrate specificities and cellular localization, contributing to a complex and multi-layered antiviral defense system. For instance, APOBEC3G is a potent inhibitor of HIV-1 replication. While APOBEC3 proteins are crucial for host defense, they can also pose a challenge to viral evolution, as viruses have developed mechanisms to counteract their activity, such as the viral infectivity factor (VIF) protein of HIV. Beyond antiviral roles, research is exploring potential involvement of APOBEC3 enzymes in other cellular processes, including DNA repair and somatic hypermutation.