Structure-based cleavage mechanism of Thermus thermophilus Argonaute DNA guide strand-mediated DNA target cleavage

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Thermus thermophilus Argonaute (TtAgo) is a key enzyme involved in nucleic acid processing.
• Understanding its mechanism is crucial for applications in biotechnology and gene editing.

Purpose of the Study:

• To elucidate the molecular mechanisms of TtAgo-mediated DNA cleavage.
• To provide high-resolution structural insights into TtAgo-DNA target interactions across different functional states.

Main Methods:

• X-ray crystallography was used to determine the structures of TtAgo ternary complexes.
• Structures were solved at resolutions up to 2.2 Å for cleavage-incompatible, cleavage-compatible, and postcleavage states.

Main Results:

• Detailed molecular insights into the positioning of catalytic residues, Mg(2+) ions, and water nucleophile for RNase H-type cleavage.
• Identified protein and DNA conformational changes enabling transitions between cleavage states.
• Revealed the role of a Glu finger in forming a catalytic tetrad (Asp-Glu-Asp-Asp).
• Observed stable duplex formation between the guide DNA seed segment and the target strand post-cleavage.

Conclusions:

• The study provides a comprehensive structural understanding of the TtAgo DNA cleavage mechanism.
• These findings highlight the dynamic nature of TtAgo and its precise catalytic machinery.
• The structural data can inform the design of engineered Argonaute proteins for precise gene manipulation.