# Structural insights into WRN helicase reveal conformational states and opportunities for MSI-H cancer drug discovery

## TL;DR

This study reveals the structural changes in WRN helicase and how inhibitors can be improved to treat MSI-H cancers.

## Contribution

The study provides crystal structures of WRN in different states and identifies how inhibitors can be optimized to target DNA-bound WRN.

## Key findings

- Crystal structures of WRN reveal conformational changes during DNA unwinding.
- Inhibitors HRO761 and VVD-133214 lock WRN in inactive states, but resistance can develop quickly.
- A structural framework for WRN's cycle is established to guide drug development.

## Abstract

Werner syndrome helicase (WRN) is a RecQ-family DNA helicase essential for genome maintenance and is a synthetic lethal target in microsatellite instability-high (MSI-H) cancers. Despite its therapeutic promise, the conformational dynamics that enable WRN to unwind DNA, and how inhibitors disrupt this activity, remains poorly understood. Here, we present crystal structures of apo WRN and WRN bound to single-stranded DNA (ssDNA), capturing key conformations in the helicase catalytic cycle. These structures reveal how WRN engages DNA through conserved polar and aromatic interactions, and how domain rearrangements, including an ordering of the aromatic-rich loop (ARL), drive directional translocation. Biochemical and biophysical data demonstrate how nucleotide and inhibitor binding remodel these conformations and suggest that known clinical inhibitors (HRO761 and VVD-133214) function by locking WRN in inactive, ‘off-DNA’ states. Resistance emerged rapidly in vitro, through acquired point mutations as well as altered WRN expression. Together, our findings provide a structural framework for the WRN structural cycle and support the development of next-generation ‘on-DNA’ inhibitors to overcome resistance.

In this study, Kennedy et al. combine crystallography, biophysical measurements and biochemical assays to define a structural cycle for Werner syndrome helicase (WRN) and reveal how nucleotide binding and ssDNA engagement lead to conformational transitions.