Mutations in human protein SLX4 (or FANCP) have been implicated in the genetic disease Fanconi anemia (FA), characterized by bone marrow failure, predisposition to cancer, and enhanced sensitivity to DNA cross-linking agents.
Recently, a research group led by Prof. LEI Ming at National Center for Protein Science·Shanghai, Institute of Biochemistry and Cell Biology (SIBCB), Shanghai Institutes for Biological Sciences (SIBS), Chinese Academy of Sciences(CAS), reported that functioning of SLX4 is critically dependent on its dimerization. This work was published in Nucleic Acids Research.
SLX4 assembles and coordinates a nuclease toolkit, consisting of the nucleases SLX1, MUS81, and XPF to function in diverse pathways of genome maintenance, including DNA interstrand cross link repair, DNA replication, nucleolytic processing of homologous recombination intermediates, management of replication stress at specific difficult-to-replicate genomic loci, and telomere maintenance. The multi-domain architecture of SLX4 enables it to not only bind to a wide range of DNA repair proteins, but also orchestrate their delivery and activities at the target site, each function mediated by one or more specific domain(s) of SLX4. Although it is known that SLX4 acts as a scaffold for building this complex, the molecular basis underlying this function of SLX4 remains unclear.
In this work, researchers identified the first crystal structure of SLX4 dimmer, identifying key contacts that are necessary and sufficient for SLX4 dimerization. They showed that disruption of SLX4 dimerization abrogates SLX4 function, for example by abolishing assembly of the functional nuclease toolkit on telomeres. This results in telomere defects arising out of aberrant telomere replication, homologous recombination, and length homeostasis, all of which have the potential to destabilize the genome. These findings will help further our understanding of the molecular basis of FA.
This work was conducted in collaboration with YIN Jinhu and his colleagues from a research group led by Prof. LIU Yie at Laboratory of Molecular Gerontology, National Institute on Aging/National Institute of Health.
This study entitled “Dimerization of SLX4 contributes to functioning of the SLX4-nuclease complex” was published online in Nucleic Acids Research on April 29, 2016.
This work was supported by the Intramural Research Program of the National Institutes of Health, National Institute on Aging, and by the grants from the Ministry of Science and Technology of China, the National Natural Science Foundation of China, and the Strategic Priority Research Program of the Chinese Academy of Sciences.
AUTHOR CONTACT:
LEI Ming, Principal Investigator
Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
Email: leim@sibcb.ac.cn
KEYWORDS:
Fanconi anemia, Nuclease, Telomere, SLX4, Dimerization
NEWS ABSTRACT:
The Fanconi anemia protein SLX4 assembles a genome and telomere maintenance toolkit, consisting of the nucleases SLX1, MUS81, and XPF. Although it is known that SLX4 acts as a scaffold for building this complex, the molecular basis underlying this function of SLX4 remains unclear. Researchers led by Prof. LEI Ming report that functioning of SLX4 is critically dependent on its dimerization, revealing the contribution of BTB domain-mediated dimerization of SLX4 in genome and telomere maintenance. These findings will help further our understanding of the molecular basis of Fanconi anemia.
Figure. Molecular basis of SLX4 dimerization in functioning of SLX4-nuclease complex. (A) Schematic showing domain mapping of human SLX4 protein. ZF, ubiquitin-binding zinc finger domain; XBR, XPF-binding region; BTB, Bric-a-brac, Tramtrack and Broad complex domain; TBM, TRF2-binding motif; SIM: SUMO-Interacting Motif; SAP, SAP motif, MUS81-binding region; SBD, SLX1-binding domain. (B) Overall structure of dimeric SLX4BTB. The monomers are colored in cyan and yellow. (C) SLX4BTB mutants impair oligomerization of SLX4 in cells. (D) Representative IF images, showing nuclear foci formation and colocalization of moderately expressed GFP-SLX4 (wild type or mutants) with TRF2 in SLX4-depleted U2OS cells. Bar: 5 mm. (E) Representative IF-FISH images, showing that the nuclease XPF form discrete nuclear foci that colocalize with SLX4 foci and telomeres in U2OS cells expressing wild type SLX4, but not in SLX4∆BTB, SLX4F708R, SLX4F681R/F708R, and SLX4F681R/F708R/L1022A mutants. (Image provided by Prof. LEI Ming’s lab)
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