Divergence in Dimerization and Activity of Primate APOBEC3C

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• APOBEC3 (A3) proteins are host restriction factors inhibiting lentiviruses like HIV-1.
• The Vif protein of HIV-1 counteracts A3 restriction by causing A3 degradation.
• APOBEC3C (A3C) orthologs in higher primates are more active than human A3C, while Old World Monkey A3C, such as rhesus macaque A3C (rhA3C), exhibits reduced activity.

Purpose of the Study:

• To determine the molecular basis for the reduced antiviral activity of rhA3C against HIV-1 compared to human A3C.
• To identify key amino acid residues and structural features governing rhA3C dimerization and antiviral function.
• To analyze the coevolution of the A3C dimerization interface and predict antiviral activity in other Old World Monkey A3C proteins.

Main Methods:

• Biochemical assays to assess deaminase activity.
• Virological studies to evaluate antiviral potency against HIV-1.
• Coevolutionary analyses to trace sequence changes in A3C orthologs.
• Molecular dynamics simulations to investigate protein dynamics and interactions.
• Site-directed mutagenesis to identify key amino acid residues.

Main Results:

• Specific amino acids (44, 45, and 144) in rhA3C were identified as crucial for its limited antiviral activity, promoting dimerization and altering loop dynamics near the active site.
• Forced evolution of rhA3C created a dimer interface similar to hominid A3C, but with distinct key amino acid contacts.
• rhA3C demonstrates significantly lower activity against HIV-1 compared to human A3C, with identified residues explaining this difference.
• Coevolutionary analysis suggests that other Old World Monkey A3Cs likely lack anti-lentiviral activity despite possessing some residues important for hominid A3C function.

Conclusions:

• The reduced antiviral activity of rhA3C is attributed to specific amino acid substitutions affecting its dimerization interface and enzyme dynamics.
• The study establishes a network of amino acids critical for A3C dimerization and enhanced activity, providing insights into primate lentiviral restriction.
• Findings predict a lack of anti-lentiviral activity in other Old World Monkey A3Cs, offering a framework for analyzing A3 family member dimerization.