Mechanism for autoinhibition and activation of the MORC3 ATPase

Abstract

Microrchidia 3 (MORC3) is a human protein linked to autoimmune disorders, Down syndrome, and cancer. It is a member of a newly identified family of human ATPases with an uncharacterized mechanism of action. Here, we elucidate the molecular basis for inhibition and activation of MORC3. The crystal structure of the MORC3 region encompassing the ATPase and CW domains in complex with a nonhydrolyzable ATP analog demonstrates that the two domains are directly coupled. The extensive ATPase:CW interface stabilizes the protein fold but inhibits the catalytic activity of MORC3. Enzymatic, NMR, mutational, and biochemical analyses show that in the autoinhibited, off state, the CW domain sterically impedes binding of the ATPase domain to DNA, which in turn is required for the catalytic activity. MORC3 autoinhibition is released by disrupting the intramolecular ATPase:CW coupling through the competitive interaction of CW with histone H3 tail or by mutating the interfacial residues. Binding of CW to H3 leads to a marked rearrangement in the ATPase–CW cassette, which frees the DNA-binding site in active MORC3 (on state). We show that ATP-induced dimerization of the ATPase domain is strictly required for the catalytic activity and that the dimeric form of ATPase–CW might cooperatively bind to dsDNA. Together, our findings uncovered a mechanism underlying the fine-tuned regulation of the catalytic domain of MORC3 by the epigenetic reader, CW.

Molecular mechanism of the MORC4 ATPase activation

“…The structure reveals a symmetric parallel homodimer with each ATPaseCW protomer coordinating one molecule of AMPPNP and one Mg 2+ ion. The ATPase module folds into the GHKL-type domain, consisting of a mixture of α-helices and β-strands, and is involved in the formation of a large dimer interface, which was also observed in the respective structures of MORC3 and MORC2 14,15,17 . Two zincbinding CW domains tightly pack against the ATPase domains and are positioned on the sides of the ATPase domains opposite to the dimer interface and are far apart (colored yellow in Fig.…”

“…Strikingly, while the MORC4 ATPaseCW cassette structure superimposes well with the structure of ATPaseCW in the homologous protein MORC3 15 (RMSD of 1.5 Å) and shares high sequence similarity with MORC3 ( Supplementary Fig. 3), the mechanisms of action of the two proteins differ.…”

“…Although the ability of MORC4 to hydrolyze ATP has not been investigated, the homologous MORC proteins, such as MORC2 and MORC3 are enzymatically active. MORC3 has been shown to exist in an autoinhibited state and is activated through binding to methylated histone mark H3K4me3, associated with transcriptionally active chromatin [12][13][14][15][16] . Conversely, MORC2 does not recognize H3K4me3 and is necessary for the human silencing hub (HUSH)-dependent silencing of transgenes integrated at chromatin loci with the methylated histone mark H3K9me3 17,18 .…”

“…1a). Recognition of H3K4me3 by MORC3 is mediated by the CW domain, and this interaction regulates the catalytic activity of MORC3 and is required for the MORC3 recruitment to chromatin and formation of liquid-liquid phase separation (LLPS) droplets in the nucleus 13,15,19,20 . While we have begun understanding the markedly different mechanisms of action and some biological roles of the individual MORC2 and MORC3 proteins, virtually nothing is known about the function of MORC4.…”

<p>Diagnostic Significance of Downregulated circMORC3 as a Molecular Biomarker of Hypopharyngeal Squamous Cell Carcinoma: A Pilot Study</p>

“…MORC family CW-type zinc finger 3 (MORC3) belongs to a new family of ATPases, MORCs, which participate in various cancers. 22,23 MORC3 expression changed after anticancer chemotherapy, suggesting that MORC3 was involved in reactions to cellular damage caused by chemotherapy. 24 And by recruiting p53 and localizing it to promyelocytic leukemia nuclear bodies (PML-NBs), MORC3 plays essential roles in p53-induced cellular senescence.…”