Probing the molecular function of RecQ4 in human Genome Integrity

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Maintenance of genomic integrity is vital for every organism to preserve cellular functions and prevent cancer and aging. The family of RecQ helicases represents an essential component of the genome maintenance system. Its members operate in virtually all DNA metabolism pathways, including DNA replication, DNA repair and telomere maintenance. Of the five RecQ helicases found in humans, RecQ4 assumes a special position as it lacks several RecQ characteristics domains, which have been shown to be indispensible for functionality in other RecQ helicases. Furthermore, RecQ4 is the only RecQ family member which is also present in mitochondria in addition to the nucleus. Loss of function mutations in RecQ4 lead to the development of the three human pathologies Rothmund Thomson Syndrome type II, RAPADILINO syndrome and Baller Gerold Syndrome, characterized by a combination of developmental defects, skeletal abnormalities, a predisposition to cancer and/or premature aging phenotypes. Intriguingly, RecQ4 upregulation is also associated with carcinogenesis and metastasis. We solved the structure of the RecQ4 helicase and showed that it contains a unique domain within its C terminus that likely represents a module for the interaction with other proteins and/or specific non standard DNA substrates. Our biochemical data indicate that RecQ4 might utilize an atypical helicase mechanism, whose function is facilitated by the very C terminal amino acids. In order to elucidate the molecular basis of this uncommon mechanism we will structurally and functionally characterize RecQ4 with its C terminus in complex with different DNA substrates. To decipher the functional role of our newly discovered domain, we will conduct binding studies with non standard DNA substrates, such as Holiday Junctions, Displacement loops and G quadruplex DNA, all of which resemble naturally occurring DNA metabolism intermediates, and examine if and how RecQ4 could process such DNA structures. The molecular framework of how RecQ4 facilitates genomic maintenance is only beginning to emerge. Thus, we will structurally and functionally characterize the binding between RecQ4 and three important DNA maintenance related binding partners: PARP 1, p53 and XPA. After determining the minimal interaction complexes, which will be utilized for structural studies, we will probe the functional collaboration between the binding partners, both in vitro and in vivo. The analysis of the atypical helicase mechanism of RecQ4 in combination with functional interaction studies addressing important genome maintenance related DNA substrates as well as binding partners will provide important insights into the role of RecQ4 in genome maintenance and the origin of RecQ4 associated human pathologies.