MS06-P02 Structural basis of ASPL-mediated regulation of p97 methylation by METTL21DThe ATPase p97/VCP (valosin containing protein) belongs to the family of AAA+ proteins (ATPases associated with diverse cellular activities). This essential and conserved protein family is involved in a broad range of cellular processes, such as DNA repair, cell cycle regulation, transcriptional activation, recombination, organelle biogenesis, ubiquitin‐mediated protein degradation and homotypic membrane fusion (1). The function of p97 is regulated by a number of adaptor proteins and post-translational modifications (2). One example is the adaptor protein ASPL (alveolar soft-part locus), that has been investigated in further detail in our group, biochemically and structurally, showing that ASPL regulates p97 activity by reassembling it from a hexamer into a heterotetrameric complex containing two monomers of p97 and two molecules of ASPL (3).
The METTL21 family of methyltransferases is a novel class of methyltransferases dedicated to methylation of chaperones. METTL21D, also known as VCP-lysine methyltransferase (VCP-KMT), trimethylates p97 specifically at Lys315 (4). Overexpression of METTL21D has been shown to be present in number of human tumor tissues and able to increase the metastatic migration capability of several METTL21D knockout cancer cell lines (5). Trimethylated Lys315 is ubiquitously present in the intact hexameric form of endogenous p97 inside the pore, but it is inaccessible to METTL21D. ASPL promotes methylation (6) by disassembling the hexameric form of p97, thereby creating a new interaction interface for METTL21D.
Here we present the first crystal structure of a methyltransferase from the METLL21 family, METTL21D, bound to its target chaperone p97 in presence of its remodeling adaptor protein ASPL, adenosine-diphosphate (ADP) and the cofactor S-adenosyl-L-methionine (SAM). The structure reveals that METTL21D binds to the highly conserved second region of homology (SRH) motif of monomeric p97, in close proximity of the target site Lys315. The SRH motif serves as a recognition sequence for METTL21D, but the interaction extends to a larger surface of the D1 domain of p97. The structure shows the importance of p97 remodeling by ASPL and potentially other remodeling adaptor proteins to enable modification of inaccessible residues and to create new interaction interfaces.References:
1. Stach, L. & Freemont, P. S. The AAA+ ATPase p97, a cellular multitool. Biochem. J. 474, 2953–2976 (2017).
2. Hänzelmann, P. & Schindelin, H. The Interplay of Cofactor Interactions and Post-translational Modifications in the Regulation of the AAA+ ATPase p97. Front. Mol. Biosci. 4, 1–22 (2017).
3. Arumughan, A. et al. Quantitative interaction mapping reveals an extended UBX domain in ASPL that disrupts functional p97 hexamers. Nat. Commun. 7, 13047 (2016).
4. Kernstock, S. et al. Lysine methylation of VCP by a member of a novel human protein methyltransferase family. Nat. Commun. 3, (2012).
5. Thiele, W. et al. Discovery of a novel tumour metastasis-promoting gene, NVM-1. J. Pathol. 225, 96–105 (2011).
6. Cloutier, P. et al. A Newly Uncovered Group of Distantly Related Lysine Methyltransferases Preferentially Interact with Molecular Chaperones to Regulate Their Activity. PLoS Genet. 9, (2013).Keywords: p97 regulation, reassembly, methylation