Harmonin homology domain-mediated interaction of RTEL1 helicase with RPA and DNA provides mechanistic insight into its role in DNA repair

Abstract

Regulator of telomere elongation helicase 1 (RTEL1) is an Fe-S cluster containing helicase that plays important roles in telomere DNA maintenance, DNA repair, and genome stability. It is a modular protein comprising a helicase domain, two tandem harmonin homology domains 1 & 2 (HHD1 and HHD2), and a RING domain. The RING domain interacts with telomere DNA binding protein TRF2 and helps in the recruitment of RTEL1 to the telomeres while the helicase domain disassembles telomere DNA t/D-loop and unwinds G-quadruplexes. The novel HHDs are predicted to mediate protein-protein interactions. Mutations in RTEL1 are associated with Hoyeraal-Hreidarsson syndrome and familial pulmonary fibrosis. Several of these mutations are found in the HHDs of RTEL1. In this study, we have carried out the structural characterization of HHDs of RTEL1. We report that human RTEL1 interacts and co-localizes with the replication protein A (RPA) in the cell. Using NMR spectroscopy and ITC experiments, we have shown that the HHD2 of RTEL1 interacts directly with the winged-helix 32C domain of RPA as well as DNA using an overlapping surface. These results establish an interplay among RTEL1, RPA, and DNA that has implications for understanding the role of RTEL1 in DNA replication, repair, and recombination processes.

Crystal structure of the HHD2 domain in human RTEL1

“…Recently Niranja Kumar et al also determined the structure of HHD2 domain (Kumar et al, 2024). When superimposed, our human HHD2 domain (PDB ID: 8YA8) structure and Niranja to each other (Table 1).…”

“…Due to its G-rich sequence, TERRA can form stable, four-stranded structures known as G-quadruplexes in vitro (Bao and Xu, 2018). The recent study also demonstrated that Replication protein A (RPA) utilizes its 32C domain to engage with the HHD2 domain of RTEL1 (Kumar et al, 2024). Many mutations in RTEL1 have been associated with genetic disorders.…”