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Marc Kschonsak

Bio: Marc Kschonsak is an academic researcher from Genentech. The author has contributed to research in topics: Exome sequencing & Chromatin remodeling. The author has an hindex of 4, co-authored 5 publications receiving 35 citations.

Papers
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Journal ArticleDOI
TL;DR: Surprisingly, a few SMARCA4 missense variants partially or fully rescued paralog dependency are found, underscoring that careful selection criteria must be employed to identify patients with inactivating, homozygousSMARCA 4 missense mutations who may benefit from SMAR CA2-targeted therapy.
Abstract: Genomic studies performed in cancer patients and tumor-derived cell lines have identified a high frequency of alterations in components of the mammalian switch/sucrose non-fermentable (mSWI/SNF or BAF) chromatin remodeling complex, including its core catalytic subunit, SMARCA4. Cells exhibiting loss of SMARCA4 rely on its paralog, SMARCA2, making SMARCA2 an attractive therapeutic target. Here we report the genomic profiling of solid tumors from 131,668 cancer patients, identifying 9434 patients with one or more SMARCA4 gene alterations. Homozygous SMARCA4 mutations were highly prevalent in certain tumor types, notably non-small cell lung cancer (NSCLC), and associated with reduced survival. The large sample size revealed previously uncharacterized hotspot missense mutations within the SMARCA4 helicase domain. Functional characterization of these mutations demonstrated markedly reduced remodeling activity. Surprisingly, a few SMARCA4 missense variants partially or fully rescued paralog dependency, underscoring that careful selection criteria must be employed to identify patients with inactivating, homozygous SMARCA4 missense mutations who may benefit from SMARCA2-targeted therapy. SMARCA4 is the core catalytic subunit of the mammalian SWI/SNF complex and is known to be mutated in many cancers. Here, the authors detect more than 10,000 SMARCA4 variants across different cancer subtypes and find hotspot mutations throughout the helicase domain, which reduce remodeling activity.

41 citations

Journal ArticleDOI
22 Jul 2020-Nature
TL;DR: Structural and functional studies of the sodium leak channel, non-selective (NALCN) in complex with a distinct auxiliary subunit reveal the structural basis of the channel function and pharmacology and the functional impact of mutations that cause NALCN channelopathies.
Abstract: Persistently depolarizing sodium (Na+) leak currents enhance electrical excitability1,2. The ion channel responsible for the major background Na+ conductance in neurons is the Na+ leak channel, non-selective (NALCN)3,4. NALCN-mediated currents regulate neuronal excitability linked to respiration, locomotion and circadian rhythm4–10. NALCN activity is under tight regulation11–14 and mutations in NALCN cause severe neurological disorders and early death15,16. NALCN is an orphan channel in humans, and fundamental aspects of channel assembly, gating, ion selectivity and pharmacology remain obscure. Here we investigate this essential leak channel and determined the structure of NALCN in complex with a distinct auxiliary subunit, family with sequence similarity 155 member A (FAM155A). FAM155A forms an extracellular dome that shields the ion-selectivity filter from neurotoxin attack. The pharmacology of NALCN is further delineated by a walled-off central cavity with occluded lateral pore fenestrations. Unusual voltage-sensor domains with asymmetric linkages to the pore suggest mechanisms by which NALCN activity is modulated. We found a tightly closed pore gate in NALCN where the majority of missense patient mutations cause gain-of-function phenotypes that cluster around the S6 gate and distinctive π-bulges. Our findings provide a framework to further study the physiology of NALCN and a foundation for discovery of treatments for NALCN channelopathies and other electrical disorders. Structural and functional studies of the sodium leak channel, non-selective (NALCN) in complex with a distinct auxiliary subunit reveal the structural basis of the channel function and pharmacology and the functional impact of mutations that cause NALCN channelopathies.

33 citations

Journal ArticleDOI
04 Mar 2021-Cell
TL;DR: In this article, the authors determine three cryogenic electron microscopy (cryo-EM) structures of the trimer and the details of its interactions with four binding partners: the receptor proteins PDGFRα and TGFβR3 as well as two broadly neutralizing antibodies.

27 citations

Journal ArticleDOI
TL;DR: A streamlined protocol for reconstituting a yeast centromeric nucleosome and a systematic exploration of cryo-grid preparation are described and a high-resolution cryoelectron microscopy reconstruction is obtained.

16 citations

Journal ArticleDOI
TL;DR: A new investment will expand the effort in cryo-EM by incorporating in the facility by 2020 a Glacios microscope fitted with a K2 direct detector (Gatan, Pleasanton, CA) and an additional Titan Krios’ equipped with a BioQuantum energy filter and a K3 direct detector.
Abstract: An initial strategic investment in cryo-EM infrastructures in 2015, completed by late 2017, enable our facility to accommodate two microscopes: a Talos 200C screening microscope (ThermoFisher Scientific, Waltham, MA), equipped with 4K Ceta-D CMOS detector and a Titan Krios G2 (ThermoFisher Scientific, Waltham, MA) fitted with K2 summit direct detector equipped with a BioQuantum energy filter (Gatan, Pleasanton, CA). These infrastructures were key in supporting several small molecule pipeline projects with high-resolution structure and medicinal chemistry design. Following this success, a new investment will expand our effort in cryo-EM by incorporating in our facility by 2020 a Glacios microscope (ThermoFisher Scientific, Waltham, MA) fitted with a K2 direct detector (Gatan, Pleasanton, CA) and an additional Titan Krios’ equipped with a BioQuantum energy filter and a K3 direct detector (Gatan, Pleasanton, CA).

2 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a review of the principles behind various techniques in the preparation of vitrified samples for the electron microscope is presented, from sample optimization and carriers to deposition and vitrification.
Abstract: Cryo-electron microscopy (cryo-EM) is rapidly becoming an attractive method in the field of structural biology. With the exploding popularity of cryo-EM, sample preparation must evolve to prevent congestion in the workflow. The dire need for improved microscopy samples has led to a diversification of methods. This Review aims to categorize and explain the principles behind various techniques in the preparation of vitrified samples for the electron microscope. Various aspects and challenges in the workflow are discussed, from sample optimization and carriers to deposition and vitrification. Reliable and versatile specimen preparation remains a challenge, and we hope to give guidelines and posit future directions for improvement. The quality of structural data obtained in cryo-EM is affected by multiple factors pertaining to sample preparation. This Review discusses available techniques and current challenges.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the authors collected clinicopathologic and genomic data from patients with NSCLC who underwent targeted next-generation sequencing at the Dana-Farber Cancer Institute and characterized the presence or absence of muts across a set of six SWI/SNF genes.

37 citations

Journal ArticleDOI
TL;DR: In this article , the authors demonstrate cell-type specificity in the tumor-suppressive functions of SMARCA4 in the lung, pointing toward a critical role of the cell-of-origin in driving SWI/SNF-mutant lung adenocarcinoma.
Abstract: SMARCA4/BRG1 encodes for one of two mutually exclusive ATPases present in mammalian SWI/SNF chromatin remodeling complexes and is frequently mutated in human lung adenocarcinoma. However, the functional consequences of SMARCA4 mutation on tumor initiation, progression, and chromatin regulation in lung cancer remain poorly understood. Here, we demonstrate that loss of Smarca4 sensitizes club cell secretory protein-positive cells within the lung in a cell type-dependent fashion to malignant transformation and tumor progression, resulting in highly advanced dedifferentiated tumors and increased metastatic incidence. Consistent with these phenotypes, Smarca4-deficient primary tumors lack lung lineage transcription factor activities and resemble a metastatic cell state. Mechanistically, we show that Smarca4 loss impairs the function of all three classes of SWI/SNF complexes, resulting in decreased chromatin accessibility at lung lineage motifs and ultimately accelerating tumor progression. Thus, we propose that the SWI/SNF complex via Smarca4 acts as a gatekeeper for lineage-specific cellular transformation and metastasis during lung cancer evolution. SIGNIFICANCE: We demonstrate cell-type specificity in the tumor-suppressive functions of SMARCA4 in the lung, pointing toward a critical role of the cell-of-origin in driving SWI/SNF-mutant lung adenocarcinoma. We further show the direct effects of SMARCA4 loss on SWI/SNF function and chromatin regulation that cause aggressive malignancy during lung cancer evolution.This article is highlighted in the In This Issue feature, p. 275.

37 citations

Journal ArticleDOI
TL;DR: In this article , the authors describe advances in antibody discovery and engineering that have led to the development of mAbs for use against infections caused by viruses including SARS-CoV-2, respiratory syncytial virus (RSV), Ebola virus (EBOV), human cytomegalovirus (HCMV), and influenza.
Abstract: Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections owing to characteristics such as their high specificity and their ability to enhance immune responses. Furthermore, antibody engineering can be used to strengthen effector function and prolong mAb half-life, and advances in structural biology have enabled the selection and optimization of potent neutralizing mAbs through identification of vulnerable regions in viral proteins, which can also be relevant for vaccine design. The COVID-19 pandemic has stimulated extensive efforts to develop neutralizing mAbs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with several mAbs now having received authorization for emergency use, providing not just an important component of strategies to combat COVID-19 but also a boost to efforts to harness mAbs in therapeutic and preventive settings for other infectious diseases. Here, we describe advances in antibody discovery and engineering that have led to the development of mAbs for use against infections caused by viruses including SARS-CoV-2, respiratory syncytial virus (RSV), Ebola virus (EBOV), human cytomegalovirus (HCMV) and influenza. We also discuss the rationale for moving from empirical to structure-guided strategies in vaccine development, based on identifying optimal candidate antigens and vulnerable regions within them that can be targeted by antibodies to result in a strong protective immune response. Monoclonal antibodies (mAbs) are appealing as potential therapeutics and prophylactics for viral infections. This Review describes advances in antibody discovery and engineering that have led to the development of mAbs that target viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), respiratory syncytial virus and Ebola virus, and also considers the implications for vaccine development.

35 citations

Journal ArticleDOI
01 Jan 2021
TL;DR: Targets brought into the realm of structure-based drug design by cryo-EM and are thus reviewed here include membrane proteins like the GABAA receptor, several TRP channels, and G protein-coupled receptors, and multiprotein complexes like the ribosomes, the proteasome, and eIF2B.
Abstract: Single-particle cryogenic electron microscopy (cryo-EM) has been elevated to the mainstream of structural biology propelled by technological advancements in numerous fronts, including imaging analysis and the development of direct electron detectors. The drug discovery field has watched with (initial) skepticism and wonder at the progression of the technique and how it revolutionized the molecular understanding of previously intractable targets. This article critically assesses how cryo-EM has impacted drug discovery in diverse therapeutic areas. Targets that have been brought into the realm of structure-based drug design by cryo-EM and are thus reviewed here include membrane proteins like the GABAA receptor, several TRP channels, and G protein-coupled receptors, and multiprotein complexes like the ribosomes, the proteasome, and eIF2B. We will describe these studies highlighting the achievements, challenges, and caveats.

33 citations