Molecular mechanism for regulating APOBEC3G DNA editing function by the non-catalytic domain.

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• APOBEC3G (apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like 3G) is a key enzyme in innate antiviral immunity.
• It possesses two distinct domains: a nucleic acid-binding N-terminal domain and a catalytic C-terminal domain responsible for C-to-U editing.
• The functional interplay between these domains remains incompletely understood.

Purpose of the Study:

• To investigate the mechanism by which APOBEC3G's DNA editing activity is modulated.
• To elucidate the role of specific DNA sequence motifs and secondary structures in APOBEC3G function.
• To understand the structural basis for APOBEC3G's interaction with DNA, particularly concerning its antiviral and mutagenic roles.

Main Methods:

• Biochemical assays to assess DNA editing activity of rhesus macaque APOBEC3G.
• Co-crystallography to determine the structure of APOBEC3G bound to DNA substrates.
• Analysis of DNA secondary structure's influence on enzyme-substrate interactions.

Main Results:

• DNA editing by rhesus macaque APOBEC3G is significantly enhanced by downstream AA or GA dinucleotide motifs.
• The distance and effectiveness of AA/GA motif enhancement are dependent on local DNA secondary structure.
• Co-crystal structures reveal the N-terminal domain's crucial role in binding these AA/GA motifs on single-stranded DNA.
• These findings highlight a cooperative mechanism involving both APOBEC3G domains.

Conclusions:

• APOBEC3G exhibits sequence-dependent DNA editing enhancement mediated by its N-terminal domain.
• This cooperative function is vital for APOBEC3G's antiviral activity.
• The elucidated mechanism provides insight into APOBEC3G's role in generating mutations observed in cancer genomes.