MORC2 phosphorylation fine tunes its DNA compaction activity.bioRxiv : the preprint server for biology • July 09, 2024
Winnie Tan, Jeongveen Park, Hariprasad Venugopal, Jieqiong Lou, Prabavi Dias, Pedro Baldoni, Kyoung-wook Moon, Toby Dite, Christine Keenan, Alexandra Gurzau, Joonyoung Lee, Timothy Johanson, Andrew Leis, Jumana Yousef, Vineet Vaibhav, Laura Dagley, Ching-seng Ang, Laura Corso, Chen Davidovich, Stephin Vervoort, Gordon Smyth, Marnie Blewitt, Rhys Allan, Elizabeth Hinde, Sheena D'arcy, Je-kyung Ryu, Shabih Shakeel
The Microrchidia (MORC) family of chromatin-remodelling ATPases is pivotal in forming higher-order chromatin structures that suppress transcription. The exact mechanisms of MORC-induced chromatin remodelling have been elusive. Here, we report an in vitro reconstitution of full-length MORC2, the most commonly mutated MORC member, linked to various cancers and neurological disorders. MORC2 possesses multiple DNA-binding sites that undergo structural rearrangement upon DNA binding. MORC2 locks onto the DNA using its C-terminal domain (CTD) and acts as a clamp. A conserved phosphate-interacting motif within the CTD was found to regulate ATP hydrolysis and cooperative DNA binding. Importantly, MORC2 mediates chromatin remodelling via ATP hydrolysis-dependent DNA compaction in vitro, regulated by the phosphorylation state of its CTD. These findings position MORC2 CTD phosphorylation as a critical regulator of chromatin remodelling and a promising therapeutic target.
SMCHD1 has separable roles in chromatin architecture and gene silencing that could be targeted in disease.Nature Communications • May 10, 2021
Andres Tapia Del Fierro, Bianca Den Hamer, Natalia Benetti, Natasha Jansz, Kelan Chen, Tamara Beck, Hannah Vanyai, Alexandra Gurzau, Lucia Daxinger, Shifeng Xue, Thanh Thao Ly, Iromi Wanigasuriya, Megan Iminitoff, Kelsey Breslin, Harald Oey, Yvonne Krom, Dinja Van Der Hoorn, Linde Bouwman, Timothy Johanson, Matthew Ritchie, Quentin Gouil, Bruno Reversade, Fabrice Prin, Timothy Mohun, Silvère Van Der Maarel, Edwina Mcglinn, James Murphy, Andrew Keniry, Jessica De Greef, Marnie Blewitt
The interplay between 3D chromatin architecture and gene silencing is incompletely understood. Here, we report a novel point mutation in the non-canonical SMC protein SMCHD1 that enhances its silencing capacity at endogenous developmental targets. Moreover, it also results in enhanced silencing at the facioscapulohumeral muscular dystrophy associated macrosatellite-array, D4Z4, resulting in enhanced repression of DUX4 encoded by this repeat. Heightened SMCHD1 silencing perturbs developmental Hox gene activation, causing a homeotic transformation in mice. Paradoxically, the mutant SMCHD1 appears to enhance insulation against other epigenetic regulators, including PRC2 and CTCF, while depleting long range chromatin interactions akin to what is observed in the absence of SMCHD1. These data suggest that SMCHD1's role in long range chromatin interactions is not directly linked to gene silencing or insulating the chromatin, refining the model for how the different levels of SMCHD1-mediated chromatin regulation interact to bring about gene silencing in normal development and disease.
SMCHD1's ubiquitin-like domain is required for N-terminal dimerization and chromatin localization.The Biochemical Journal • April 21, 2021
Alexandra Gurzau, Christopher Horne, Yee-foong Mok, Megan Iminitoff, Tracy Willson, Samuel Young, Marnie Blewitt, James Murphy
Structural maintenance of chromosomes flexible hinge domain-containing 1 (SMCHD1) is an epigenetic regulator that mediates gene expression silencing at targeted sites across the genome. Our current understanding of SMCHD1's molecular mechanism, and how substitutions within SMCHD1 lead to the diseases, facioscapulohumeral muscular dystrophy (FSHD) and Bosma arhinia microphthalmia syndrome (BAMS), are only emerging. Recent structural studies of its two component domains - the N-terminal ATPase and C-terminal SMC hinge - suggest that dimerization of each domain plays a central role in SMCHD1 function. Here, using biophysical techniques, we demonstrate that the SMCHD1 ATPase undergoes dimerization in a process that is dependent on both the N-terminal UBL (Ubiquitin-like) domain and ATP binding. We show that neither the dimerization event, nor the presence of a C-terminal extension past the transducer domain, affect SMCHD1's in vitro catalytic activity as the rate of ATP turnover remains comparable to the monomeric protein. We further examined the functional importance of the N-terminal UBL domain in cells, revealing that its targeted deletion disrupts the localization of full-length SMCHD1 to chromatin. These findings implicate UBL-mediated SMCHD1 dimerization as a crucial step for chromatin interaction, and thereby for promoting SMCHD1-mediated gene silencing.
Crystal structure of the hinge domain of Smchd1 reveals its dimerization mode and nucleic acid-binding residues.Science Signaling • June 18, 2020
Kelan Chen, Richard Birkinshaw, Alexandra Gurzau, Iromi Wanigasuriya, Ruoyun Wang, Megan Iminitoff, Jarrod Sandow, Samuel Young, Patrick Hennessy, Tracy Willson, Denise Heckmann, Andrew Webb, Marnie Blewitt, Peter Czabotar, James Murphy
Structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) is an epigenetic regulator in which polymorphisms cause the human developmental disorder, Bosma arhinia micropthalmia syndrome, and the degenerative disease, facioscapulohumeral muscular dystrophy. SMCHD1 is considered a noncanonical SMC family member because its hinge domain is C-terminal, because it homodimerizes rather than heterodimerizes, and because SMCHD1 contains a GHKL-type, rather than an ABC-type ATPase domain at its N terminus. The hinge domain has been previously implicated in chromatin association; however, the underlying mechanism involved and the basis for SMCHD1 homodimerization are unclear. Here, we used x-ray crystallography to solve the three-dimensional structure of the Smchd1 hinge domain. Together with structure-guided mutagenesis, we defined structural features of the hinge domain that participated in homodimerization and nucleic acid binding, and we identified a functional hotspot required for chromatin localization in cells. This structure provides a template for interpreting the mechanism by which patient polymorphisms within the SMCHD1 hinge domain could compromise function and lead to facioscapulohumeral muscular dystrophy.
Relating SMCHD1 structure to its function in epigenetic silencing.Biochemical Society Transactions • June 11, 2020
Alexandra Gurzau, Marnie Blewitt, Peter Czabotar, James Murphy, Richard Birkinshaw
The structural maintenance of chromosomes hinge domain containing protein 1 (SMCHD1) is a large multidomain protein involved in epigenetic gene silencing. Variations in the SMCHD1 gene are associated with two debilitating human disorders, facioscapulohumeral muscular dystrophy (FSHD) and Bosma arhinia microphthalmia syndrome (BAMS). Failure of SMCHD1 to silence the D4Z4 macro-repeat array causes FSHD, yet the consequences on gene silencing of SMCHD1 variations associated with BAMS are currently unknown. Despite the interest due to these roles, our understanding of the SMCHD1 protein is in its infancy. Most knowledge of SMCHD1 function is based on its similarity to the structural maintenance of chromosomes (SMC) proteins, such as cohesin and condensin. SMC proteins and SMCHD1 share similar domain organisation and affect chromatin conformation. However, there are important differences between the domain architectures of SMC proteins and SMCHD1, which distinguish SMCHD1 as a non-canonical member of the family. In the last year, the crystal structures of the two key domains crucial to SMCHD1 function, the ATPase and hinge domains, have emerged. These structures reveal new insights into how SMCHD1 may bind and regulate chromatin structure, and address how amino acid variations in SMCHD1 may contribute to BAMS and FSHD. Here, we contrast SMCHD1 with canonical SMC proteins, and relate the ATPase and hinge domain structures to their roles in SMCHD1-mediated epigenetic silencing and disease.
