DNA recognition by an RNA-guided bacterial Argonaute

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Argonaute (Ago) proteins are crucial for nucleic acid recognition in prokaryotes and eukaryotes.
• Prokaryotic Marinitoga piezophila Argonaute (MpAgo) binds 5'-hydroxylated RNAs and cleaves ssRNA and ssDNA targets.

Purpose of the Study:

• To determine the crystal structure of MpAgo bound to an RNA guide and ssDNA substrate.
• To elucidate the unique target recognition and cleavage mechanisms of MpAgo.

Main Methods:

• X-ray crystallography at 3.2 Å resolution.
• Structural comparison with other Argonaute complexes.
• Analysis of mismatch tolerance in target cleavage.

Main Results:

• The crystal structure reveals a unique N-terminal domain orientation in MpAgo, creating a straight helical axis for the RNA-DNA heteroduplex.
• MpAgo displays symmetric mismatch tolerance, with cleavage efficiency reduced around the helix's center.
• This differs from other Argonautes, which show reduced cleavage with 5' guide strand mismatches.

Conclusions:

• Structural analysis of MpAgo bound to a hybrid helix advances understanding of Argonaute diversity.
• MpAgo possesses distinct target recognition and cleavage mechanisms, expanding the known repertoire of Argonaute functions.