Structural maintenance of chromosomes flexible hinge domain-containing 1 (Smchd1) plays important roles in epigenetic silencing and normal mammalian development. Recently, heterozygous mutations in SMCHD1 were found to contribute to two distinct conditions: facioscapulohumeral muscular dystrophy (FSHD) and Bosma arhinia micropthalmia syndrome (BAMS). Despite Smchd1’s essential role in epigenetic regulation, its atomic structure and the molecular mechanisms underlying its function in both a healthy and diseased state remain to be elucidated.
To provide a better understanding of Smchd1’s molecular structure and function, we have successfully expressed and purified the full-length 2007-amino acid protein. Follow-up electron microscopy analyses of the Smchd1 dimer have revealed an elongated rod-like structure that displays a high conformational flexibility, similar to that of other structural maintenance of chromosomes (SMC) proteins. Our recent findings have also revealed that Smchd1 co-purifies with DNA as well as histone 3, indicating a potential association with nucleosomes which remains to be further investigated. To assess the cellular effects of FSHD- and BAMS-associated mutations on Smchd1 function, we generated SMCHD1-knockdown HEK293 cells and performed transfection of wild-type or mutant forms of full-length Smchd1 constructs. Preliminary immunofluorescence results following transfection of the BAMS-associated S135C gain-of-function Smchd1 mutant indicate a distinct nuclear localisation pattern compared to wild-type transfected cells. We can therefore further utilise this cellular-based assay as a supporting method to assess the effects of other disease-associated mutations upon Smchd1 function, which will aid in providing a better understanding of its molecular function.