Biology subjects

Watson, E. R.

Publications and source records attributed to Watson, E. R..

5 recordsLinked to original sources

bioRxiv2022

Molecular glue CELMoD compounds are allosteric regulators of cereblon conformation

Cereblon (CRBN) is an ubiquitin ligase (E3) adaptor protein co-opted by CRBN E3 Ligase Modulatory Drugs (CELMoD) agents that target therapeutically-relevant proteins for degradation. Prior crystallographic studies defined the drug-binding site within CRBNs Thalidomide Binding Domain (TBD), but the allostery of drug-induced neosubstrate binding remains unclear. We therefore performed cryo-EM analyses of the DDB1[~]CRBN apo-complex, and compared these structures with DDB1[~]CRBN in the presence of CELMoD compounds alone and complexed with neosubstrates. Association of CELMoD compounds to the TBD is necessary and sufficient for triggering CRBN allosteric rearrangement from an "open" conformation to the canonical "closed" conformation. Importantly, the neosubstrate Ikaros only stably associates with the closed CRBN conformation, illustrating the importance of allostery for CELMoD compound efficacy, and informing structure-guided design strategies to improve therapeutic efficacy.

molecular biology↗

bioRxiv2022

How does data structure impact cell-cell similarity? Evaluating the influence of structural properties on proximity metric performance in single cell RNA-seq data

Accurately identifying cell populations is paramount to the quality of downstream analyses and overall interpretations of single-cell RNA-seq (scRNA-seq) datasets but remains a challenge. The quality of single-cell clustering depends on the proximity metric used to generate cell-to-cell distances. Accordingly, proximity metrics have been benchmarked for scRNA-seq clustering, typically with results averaged across datasets to identify a highest performing metric. However, the best-performing metric varies between studies, with the performance differing significantly between datasets. This suggests that the unique structural properties of a scRNA-seq dataset, specific to the biological system under study, has a substantial impact on proximity metric performance. Previous benchmarking studies have omitted to factor the structural properties into their evaluations. To address this gap, we developed a framework for the in-depth evaluation of the performance of 17 proximity metrics with respect to core structural properties of scRNA-seq data, including sparsity, dimensionality, cell population distribution and rarity. We find that clustering performance can be improved substantially by the selection of an appropriate proximity metric and neighbourhood size for the structural properties of a dataset, in addition to performing suitable pre-processing and dimensionality reduction. Furthermore, popular metrics such as Euclidean and Manhattan distance performed poorly in comparison to several lessor applied metrics, suggesting the default metric for many scRNA-seq methods should be re-evaluated. Our findings highlight the critical nature of tailoring scRNA-seq analyses pipelines to the system under study and provide practical guidance for researchers looking to optimise cell similarity search for the structural properties of their own data.

bioinformatics↗

bioRxiv2022

Deconstructing replicative senescence heterogeneity of human mesenchymal stem cells at single cell resolution reveals therapeutically targetable senescent cell sub-populations

Cellular senescence is characterised by a state of permanent cell cycle arrest. It is accompanied by often variable release of the so-called senescence-associated secretory phenotype (SASP) factors, and occurs in response to a variety of triggers such as persistent DNA damage, telomere dysfunction, or oncogene activation. While cellular senescence is a recognised driver of organismal ageing, the extent of heterogeneity within and between different senescent cell populations remains largely unclear. Elucidating the drivers and extent of variability in cellular senescence states is important for discovering novel targeted seno-therapeutics and for overcoming cell expansion constraints in the cell therapy industry. Here we combine cell biological and single cell RNA-sequencing approaches to investigate heterogeneity of replicative senescence in human ESC-derived mesenchymal stem cells (esMSCs) as MSCs are the cell type of choice for the majority of current stem cell therapies and senescence of MSC is a recognized driver of organismal ageing. Our data identify three senescent subpopulations in the senescing esMSC population that differ in SASP, oncogene expression, and escape from senescence. Uncovering and defining this heterogeneity of senescence states in cultured human esMSCs allowed us to identify potential drug targets that may delay the emergence of senescent MSCs in vitro and perhaps in vivo in the future.

bioinformatics↗

bioRxiv2020

Structures of the Human LONP1 Protease Reveal Regulatory Steps Involved in Protease Activation

The human mitochondrial AAA+ protein LONP1 is a critical quality control protease involved in regulating diverse aspects of mitochondrial biology including proteostasis, electron transport chain activity, and mitochondrial transcription. As such, genetic or aging-associated imbalances in LONP1 activity are implicated in the pathologic mitochondrial dysfunction associated with numerous human diseases. Despite this importance, the molecular basis for LONP1-dependent proteolytic activity remains poorly defined. Here, we solved cryo-electron microscopy structures of human LONP1 to reveal the molecular mechanism of substrate proteolysis. We show that, like bacterial Lon, human LONP1 adopts both an open and closed spiral staircase orientation dictated by the presence of substrate and nucleotide. However, unlike bacterial Lon, human LONP1 contains a second spiral staircase within its ATPase domain that engages substrate to increase interactions with the translocating peptide as it transits into the proteolytic chamber for proteolysis. Further, we show that substrate-bound LONP1 includes a second level of regulation at the proteolytic active site, wherein autoinhibition of the active site is only relieved by the presence of a peptide substrate. Ultimately, our results define a structural basis for human LONP1 proteolytic activation and activity, establishing a molecular framework to understand the critical importance of this protease for mitochondrial regulation in health and disease.

molecular biology↗

bioRxiv2019

A Protein Engineering Approach for Uncovering Cryptic Ubiquitin-binding Sites: from a Ubiquitin-Variant Inhibitor of APC/C to K48 Chain Binding

Ubiquitin-mediated proteolysis is a fundamental mechanism used by eukaryotic cells to maintain homeostasis and protein quality, and to control timing in biological processes. Two essential aspects of ubiquitin regulation are conjugation through E1-E2-E3 enzymatic cascades, and recognition by ubiquitin-binding domains. An emerging theme in the ubiquitin field is that these two properties are often amalgamated in conjugation enzymes. In addition to covalent thioester linkage to ubiquitins C-terminus for ubiquitin transfer reactions, conjugation enzymes often bind non-covalently and weakly to ubiquitin at \"exosites\". However, identification of such sites is typically empirical and particularly challenging in large molecular machines. Here, studying the 1.2 MDa E3 ligase Anaphase-Promoting Complex/Cyclosome (APC/C), which controls cell division and many aspects of neurobiology, we discover a method for identifying unexpected ubiquitin-binding sites. Using a panel of ubiquitin variants (UbVs) we identify a protein-based inhibitor that blocks ubiquitin ligation to APC/C substrates in vitro and ex vivo. Biochemistry, NMR, and cryo EM structurally define the UbV interaction, explain its inhibitory activity through binding the surface on the APC2 subunit that recruits the E2 enzyme UBE2C, and ultimately reveal that this APC2 surface is also a ubiquitin-binding exosite with preference for K48-linked chains. The results provide a new tool for probing APC/C activity, have implications for the coordination of K48-linked Ub chain binding by APC/C with the multistep process of substrate polyubiquitylation, and demonstrate the power of UbV technology for identifying cryptic ubiquitin binding sites within large multiprotein complexes.\n\nSIGNIFICANCE STATEMENTUbiquitin-mediated interactions influence numerous biological processes. These are often transient or a part of multivalent interactions. Therefore, unmasking these interactions remains a significant challenge for large, complicated enzymes such as the Anaphase-Promoting Complex/Cyclosome (APC/C), a multisubunit RING E3 ubiquitin (Ub) ligase. APC/C activity regulates numerous facets of biology by targeting key regulatory proteins for Ub-mediated degradation. Using a series of Ub variants (UbVs), we identified a new Ub-binding site on the APC/C that preferentially binds to K48-linked Ub chains. More broadly, we demonstrate a workflow that can be exploited to uncover Ub-binding sites within ubiquitylation machinery and other associated regulatory proteins to interrogate the complexity of the Ub code in biology.

biochemistry↗