Comparison of the structure of Sen1 helicase domain (PBD ID 5MZN -(52)) and the helicase domain of SETX, predicted by AI-mediated modelling using AlphaFold2. RecA1 and RecA2 domains are depicted in yellow, β-barrel in orange, and the ‘prong’ subdomain in red. In purple are highlighted the key residues responsible for ATP hydrolysis (K1969, within the Walker A motif), as well as for Mg2+ coordination (D2181, E2182, within the Walker B motif).
Prolonged pausing of the transcription machinery may lead to the formation of three-stranded nucleic acid structures, called R-loops, typically resulting from the annealing of the nascent RNA with the template DNA. Unscheduled persistence of R-loops and RNA polymerases may interfere with transcription itself and other essential processes such as DNA replication and repair. Senataxin (SETX) is a putative helicase, mutated in two neurodegenerative disorders, which has been implicated in the control of R-loop accumulation and in transcription termination. However, understanding the precise role of SETX in these processes has been precluded by the absence of a direct characterisation of SETX biochemical activities. Here, we purify and characterise the helicase domain of SETX in parallel with its yeast orthologue, Sen1. Importantly, we show that SETX is a bona fide helicase with the ability to resolve R-loops. Furthermore, SETX has retained the transcription termination activity of Sen1 but functions in a species-specific manner. Finally, subsequent characterisation of two SETX variants harbouring disease-associated mutations shed light into the effect of such mutations on SETX folding and biochemical properties. Altogether, these results broaden our understanding of SETX function in gene expression and the maintenance of genome integrity and provide clues to elucidate the molecular basis of SETX-associated neurodegenerative diseases.
Hasanová, Z., et. al.: Human senataxin is a bona fide R-loop resolving enzyme and transcription termination factor.
Nucleic Acids Res. 2023, 51, 2818–2837, https://doi.org/10.1093/nar/gkad092