Structural insights into the duplex DNA processing of TREX2

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Three prime repair exonuclease 2 (TREX2) is a 3'-to-5' exonuclease crucial for cell proliferation, genome integrity, and skin homeostasis.
• Dysregulation of TREX2 is linked to chromosomal instability, increased skin cancer susceptibility, and Psoriasis.
• The precise molecular mechanisms of TREX2 substrate binding and processing, particularly for double-stranded DNA (dsDNA), remain largely unknown.

Purpose of the Study:

• To elucidate the structural basis of TREX2 interaction with its natural dsDNA substrates.
• To understand the molecular mechanisms by which TREX2 binds and processes dsDNA for genome stability.
• To provide insights into the functional role of TREX2 in chromosomal DNA processing.

Main Methods:

• X-ray crystallography was employed to determine four new crystal structures: apo-TREX2, TREX2 with two distinct dsDNA substrates, and TREX2 with a processed dsDNA product.
• Structural analysis focused on identifying key residues and interaction motifs involved in dsDNA binding and trimming.
• Biochemical assays were implicitly used to characterize the non-processive nature of TREX2.

Main Results:

• Crystal structures reveal TREX2 utilizes a Leu20-Pro21-Asn22 cluster to stack with the 5'-terminus of dsDNA, enabling precise 3'-overhang trimming.
• Specific interactions between TREX2 and the non-scissile strand of dsDNA involve an α-helix-loop region.
• The findings indicate a requirement for a long double-stranded region for TREX2 binding and provide evidence for its role in processing chromosomal DNA.
• The structure of the TREX2-product complex elucidates the enzyme's non-processive activity.

Conclusions:

• This study provides the first structural insights into the molecular interactions between TREX2 and its dsDNA substrates.
• The elucidated mechanisms explain how TREX2 precisely trims dsDNA, contributing to genome stability.
• The findings highlight the functional significance of TREX2 in processing chromosomal DNA and maintaining skin homeostasis.