Substrate sequence selectivity of APOBEC3A implicates intra-DNA interactions.

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• The APOBEC3 (A3) protein family acts as a defense against viruses but can also cause cancer by deaminating DNA.
• The precise mechanisms governing A3 enzyme sequence specificity remain unclear.
• APOBEC3A (A3A) is implicated in endogenous DNA mutagenesis.

Purpose of the Study:

• To systematically characterize the substrate sequence specificity of A3A.
• To elucidate the molecular mechanisms behind A3A's DNA binding preferences.

Main Methods:

• Quantified A3A substrate affinity across varying sequence contexts, lengths, secondary structures, and pH.
• Utilized existing A3A-ssDNA co-crystal structures.

Main Results:

• Identified a specific ssDNA binding motif for A3A: (T/C)TC(A/G), correlating with activity.
• Confirmed sequence-specific RNA binding by A3A.
• Demonstrated higher A3A affinity for hairpin-structured DNA compared to linear forms.
• Proposed a new model for A3A sequence preference involving intra-DNA interactions.

Conclusions:

• A3A exhibits distinct sequence and structural preferences for DNA binding.
• These findings offer a new framework for understanding A3A's role in DNA mutation.
• The study advances knowledge of A3A's dual role in antiviral defense and mutagenesis.