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Structural insights into the N-terminal APHB domain of HrpA: mediating canonical and i-motif recognition.
Nucleic Acids Res, 52(6):3406-3418.
RNA helicases function as versatile enzymes primarily responsible for remodelingRNA secondary structures and organizing ribonucleoprotein complexes. In ourstudy, we conducted a systematic analysis of the helicase-related activities ofEscherichia coli HrpA and presented the structures of both its apo form and itscomplex bound with both conventional and non-canonical DNAs. Our findings revealthat HrpA exhibits NTP hydrolysis activity and binds to ssDNA and ssRNA indistinct sequence-dependent manners. While the helicase core plays an essentialrole in unwinding RNA/RNA and RNA/DNA duplexes, the N-terminal extension in HrpA,consisting of three helices referred to as the APHB domain, is crucial for ssDNAbinding and RNA/DNA duplex unwinding. Importantly, the APHB domain is implicatedin binding to non-canonical DNA structures such as G-quadruplex and i-motif, andthis report presents the first solved i-motif-helicase complex. This research notonly provides comprehensive insights into the multifaceted roles of HrpA as anRNA helicase but also establishes a foundation for further investigations intothe recognition and functional implications of i-motif DNA structures in variousbiological processes.
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