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

Abstract

The 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 Zn2+ binding RING domain. In this study, we have unravelled a novel interaction between RTEL1 and replication protein A (RPA) and shown their co-localization upon DNA damage in the cells. Using NMR spectroscopy, we show that 32C domain of RPA and DNA competitively bind with HHD2 of RTEL1. To understand the structural basis of HHD2 - 32C and HHD2 - DNA interactions, we have determined a 1.6 [A] resolution crystal structure of HHD2. NMR chemical shift perturbations-based mapping revealed the 32C and DNA binding surface on HHD2 of RTEL1. Together, these results establish an interplay among RTEL1, RPA, and DNA that provide mechanistic insights into the RTEL1 recruitment at DNA during the processes of replication, repair, and recombination.