Defining the molecular interface that connects the Fanconi anemia protein FANCM to the Bloom syndrome dissolvasome

Abstract

The RMI subcomplex (RMI1/RMI2) functions with the BLM helicase and topoisomerase IIIα in a complex called the "dissolvasome," which separates double-Holliday junction DNA structures that can arise during DNA repair. This activity suppresses potentially harmful sister chromatid exchange (SCE) events in wild-type cells but not in cells derived from Bloom syndrome patients with inactivating BLM mutations. The RMI subcomplex also associates with FANCM, a component of the Fanconi anemia (FA) core complex that is important for repair of stalled DNA replication forks. The RMI/ FANCM interface appears to help coordinate dissolvasome and FA core complex activities, but its precise role remains poorly understood. Here, we define the structure of the RMI/FANCM interface and investigate its roles in coordinating cellular DNA-repair activities. The X-ray crystal structure of the RMI core complex bound to a well-conserved peptide from FANCM shows that FANCM binds to both RMI proteins through a hydrophobic "knobsinto-holes" packing arrangement. The RMI/FANCM interface is shown to be critical for interaction between the components of the dissolvasome and the FA core complex. FANCM variants that substitute alanine for key interface residues strongly destabilize the complex in solution and lead to increased SCE levels in cells that are similar to those observed in blm-or fancm-deficient cells. This study provides a molecular view of the RMI/FANCM complex and highlights a key interface utilized in coordinating the activities of two critical eukaryotic DNA-damage repair machines.

Biochemical Activities and Genetic Functions of the Drosophila melanogaster Fancm Helicase in DNA Repair

“…and West 2009; Hoadley et al 2012). It should be noted that Drosophila Fancm has neither the ERCC4 domain nor recognizable MM1 or MM2 motifs.…”

The Dissolution of Double Holliday Junctions

“…hRPA is not the only protein found to physically associate with the carboxy-terminal extension found in higher eukaryotic RMI1. Indeed, this nonconserved region is responsible for the association of the dissolvasome complex with FANCM and RMI2 (Deans and West 2009;Yang et al 2010;Hoadley et al 2012;Manthei and Keck 2013). Among them, only RMI2 is thought to be important for the functionality of the complex in vivo (Fig.…”

Functions and regulation of the multitasking FANCM family of DNA motor proteins

“…1; Deans and West 2009). While MM1 mediates association with the FA core complex through FANCF, MM2 binds RMI1 and Topo IIIα (Deans and West 2009;Hoadley et al 2012). A deletion of either MM1 or MM2 in FANCM engenders ICL sensitivity and elevates SCEs (Deans and West 2009).…”