Project description:Volume-regulated anion channels participate in the cellular response to osmotic swelling. These membrane proteins are heteromers of LRRC8 family members whose composition determines permeation properties. Although structures of the obligatory LRRC8A subunit have previously defined the architecture of VRACs, the organization of heteromeric channels has remained elusive. Here we have closed this gap by the structural characterization of channels consisting of LRRC8A and C. Like homomeric LRRC8A, these proteins assemble as hexamers. Despite the twelve possible arrangements, we find a single predominant species with an A/C ratio of two. In this assembly, the four LRRCA subunits cluster in their preferred conformation observed in homomers as pairs of closely interacting proteins that stabilize a closed state of the channel. In contrast, the two interacting LRRC8C-subunits show a larger flexibility, underlining their role in the destabilization of the tightly packed A subunits, thereby enhancing the activation properties of the protein.
Project description:Cellular functionality relies on a well-balanced, but highly dynamic proteome. Dysfunctionof mitochondrial protein import leads to the cytosolic accumulation of mitochondrial precursor proteins which compromise cellular proteostasis and trigger the mitoprotein-induced stress response. To dissect the effects of mitochondrial dysfunction on the cellular proteome as a whole, we developed pre-post thermal proteome profiling (ppTPP). This multiplexed time-resolved proteome-wide thermal stability profiling approach with isobaric peptide tags in combination with a pulse SILAC labeling elucidated dynamic proteostasis changes in several dimensions: In addition to adaptations in protein abundance, we observed rapid modulations of the thermal stability of individual cellular proteins. Strikingly, different functional groups of proteins showed characteristic response patterns and reacted with group-specific kinetics, allowing the identification of the functional modules that are relevant for mitoprotein-induced stress. Thus, our new ppTPP approach uncovered a complex response network that orchestrates proteome homeostasis in eukaryotic cells by time-controlled adaptations of protein abundance and protein stability.
Project description:Global high-throughput phosphoproteomic profiling is increasingly being applied to cancer specimens as a means to identify the oncogenic signaling cascades responsible for promoting disease initiation and disease progression; pathways that are often invisible to genomics analysis. Hence, phosphoproteomic profiling has enormous potential to inform and improve individualized anti-cancer treatment strategies. However, to achieve the adequate phosphoproteomic depth and coverage necessary to identify the activated, and hence, targetable kinases responsible for driving oncogenic signaling pathways; affinity phosphopeptide enrichment techniques are required and often coupled with offline high-pressure liquid chromatographic (HPLC) separation prior to nanoflow liquid chromatography–tandem mass spectrometry (nLC-MS/MS). These complex and time-consuming procedures, limit the utility of phosphoproteomics for the analysis of individual cancer patient specimens in real-time, and restrict phosphoproteomics to specialized laboratories often outside of the clinical setting. To address these limitations, here we have optimized a new protocol, phospho-Heavy-labeled-spiketide FAIMS Stepped-CV DDA (pHASED), that employs online phosphoproteome deconvolution using high-field asymmetric waveform ion mobility spectrometry (FAIMS) and internal phosphopeptide standards to provide accurate label-free quantitation (LFQ) data in real-time. Compared with traditional LFQ using shotgun phosphoproteomics workflows, pHASED provided increased phosphoproteomic depth and coverage (phosphopeptides = 4,617 pHASED, 2,789 LFQ), whilst eliminating the variability associated with offline prefractionation. pHASED was optimized using tyrosine kinase inhibitor (sorafenib) resistant isogenic FLT3-mutant acute myeloid leukemia (AML) cell line models. Bioinformatic analysis identified differential activation of the Serine/threonine protein kinase ataxia-telangiectasia mutated (ATM) pathway, responsible for sensing and repairing DNA damage in sorafenib-resistant AML cell line models, thereby uncovering a potential therapeutic opportunity. Herein, we have optimized a rapid, reproducible, and flexible protocol for the characterization of complex cancer phosphoproteomes in real-time; a step towards the implementation of phosphoproteomics in the clinic to aid in the selection of anti-cancer therapies for patients.
Project description:Here we investigate the possible relationship between the propagation of epigenetic information and the developmental cell proliferation during Xenopus embryogenesis. We systemically inhibited cell proliferation during the G1/S-transition in gastrula embryos and followed their development until the tadpole stage. We quantified by mass spectrometry the abundance of a large set of histone modification states, which reflects the developmental maturation of the embryonic epigenome.
Project description:Protein synthesis-targeting agents against eIF4A activity, including rocaglates, are actively pursued as anticancer and antiviral therapies. Yet, their full effect on the translational landscape is unknown, especially with regards to up-regulated proteins and drug-activated translation factors that mediate rocaglates’ remarkable anticancer potency. Here, we investigated rocaglate-driven global translational remodeling in cancer cells. Proteomic translatome analysis by TMT-pulse-SILAC revealed an extensive repertoire of rocaglate-inducible proteins that regulate hitherto unrecognized mechanisms of cytotoxicity. As proof-of-concept, we show that GEF-H1 induction activates anti-survival RHOA/JNK signaling. Intriguingly, rocaglate responses persist in eIF4A-depleted cells. Global MATRIX survey of translation machinery adaptations to rocaglates revealed augmented translational activities of the general translation factor eEF1ε1, and the DEAD-box RNA helicase DDX17, which drive rocaglate-specific protein induction and drug response. This original unbiased proteomic interrogation of rocaglate-driven translational reprogramming transforms the current definition of rocaglates as one-dimensional eIF4A inhibitors to comprehensive remodelers of the protein synthesis landscape.