Single-nucleosome imaging unveils that condensins and nucleosome-nucleosome interactions differentially constrain chromatin to organize mitotic chromosomes.

For accurate mitotic cell division, replicated chromatin must be assembled into chromosomes and faithfully segregated into daughter cells. While protein factors like condensin play key roles in this process, it is unclear how chromosome assembly proceeds as molecular events of nucleosomes in living cells and how condensins act on nucleosomes to organize chromosomes. To approach these questions, we investigate nucleosome behavior during mitosis of living human cells using single-nucleosome tracking, combined with rapid-protein depletion technology and computational modeling. Our results show that local nucleosome motion becomes increasingly constrained during mitotic chromosome assembly, which is functionally distinct from condensed apoptotic chromatin. Condensins act as molecular crosslinkers, locally constraining nucleosomes to organize chromosomes. Additionally, nucleosome-nucleosome interactions via histone tails constrain and compact whole chromosomes. Our findings elucidate the physical nature of the chromosome assembly process during mitosis.

NMN partially rescues cuproptosis by upregulating sirt2 to increase intracellular NADPH.

Cuproptosis is characterized by lipoylated protein aggregation and loss of iron-sulfur (Fe-S) proteins, which are crucial for a wide range of important cellular functions, including DNA replication and damage repair. Sirt2 and sirt4 are lipoamidases that remove the lipoyl moiety from lipoylated proteins using nicotinamide adenine dinucleotide (NAD+) as a cofactor. However, to date, it is not clear whether nicotinamide mononucleotide (NMN), a precursor of NAD+, affects cellular sensitivity to cuproptosis. Therefore, in the current study, cuproptosis was induced by the copper (Cu) ionophore elesclomol (Es) in HeLa cells. It was also found that Es/Cu treatment increased cellular DNA damage level. On the other hand, NMN treatment partially rescued cuproptosis in a dose-dependent manner, as well as reduced cellular DNA damage level. In addition, NMN upregulated the expression of Fe-S protein POLD1, without affecting the aggregation of lipoylated proteins. Mechanistic study revealed that NMN increased the expression of sirt2 and cellular reduced nicotinamide adenine dinucleotide phosphate (NADPH) level. Overexpression of sirt2 and sirt4 did not change the aggregation of lipoylated proteins, however, sirt2, but not sirt4, increased cellular NADPH levels and partially rescued cuproptosis. Inhibition of NAD+ kinase (NADK), which is responsible for generating NADPH, abolished the rescuing function of NMN and sirt2 for Es/Cu induced cell death. Taken together, our results suggested that DNA damage is a characteristic feature of cuproptosis. NMN can partially rescue cuproptosis by upregulating sirt2, increase intracellular NADPH content and maintain the level of Fe-S proteins, independent of the lipoamidase activity of sirt2.

Improvement photothermal property of MoS2/Fe3O4/GNR nanocomposite in cancer treatment.

The objective of the present study was to develop a novel molybdenum disulfide/iron oxide/gold nanorods (MoS2/Fe3O4/GNR) nanocomposite (MFG) with different concentrations of AgNO3 solution (MFG1, MFG2, and MFG3) for topical doxorubicin (DOX) drug delivery. Then, these nanocomposites were synthesized and characterized by Fourier transform infrared (FTIR), Transmission electron microscopy (TEM), Dynamic light scattering (DLS), and Ultraviolet-visible (UV-Vis) spectroscopies to confirm their structural and optical properties. Cytotoxicity of samples on Hela cell was determined using MTT assay. Results indicated that nanocomposites possess little cytotoxicity without NIR laser irradiation. Also, the relative viabilities of Hela cells decreased when the concentration of AgNO3 solution increased in this nanocomposite. Using NIR irradiation, the relative viabilities of Hela cells decreased when the concentration of samples increased. Acridine orange/propidium iodide (PI) staining, flow cytometry were recruited to evaluate the effect of these nanocomposites on apoptosis of Hela cells. Finally, results revealed when DOX loading increased in nanocomposite, then cell viability was decreased in it. Therefore, these properties make MFG3 nanocomposite a good candidate for photothermal therapy and drug loading.

UPF3B modulates endoplasmic reticulum stress through interaction with inositol-requiring enzyme-1α.

The unfolded protein response (UPR) is a conserved and adaptive intracellular pathway that relieves the endoplasmic reticulum (ER) stress by activating ER transmembrane stress sensors. As a consequence of ER stress, the inhibition of nonsense-mediated mRNA decay (NMD) is due to an increase in the phosphorylation of eIF2α, which has the effect of inhibiting translation. However, the role of NMD in maintaining ER homeostasis remains unclear. In this study, we found that the three NMD factors, up-frameshift (UPF)1, UPF2, or UPF3B, were required to negate the UPR. Among these three NMD factors, only UPF3B interacted with inositol-requiring enzyme-1α (IRE1α). This interaction inhibited the kinase activity of IRE1α, abolished autophosphorylation, and reduced IRE1α clustering for ER stress. BiP and UPF3B jointly control the activation of IRE1α on both sides of the ER membrane. Under stress conditions, the phosphorylation of UPF3B was increased and the phosphorylated sites were identified. Both the UPF3BY160D genetic mutation and phosphorylation at Thr169 of UPF3B abolished its interaction with IRE1α and UPF2, respectively, leading to activation of ER stress and NMD dysfunction. Our study reveals a key physiological role for UPF3B in the reciprocal regulatory relationship between NMD and ER stress.

Dual-modified penetratin peptides: Enhancing nucleic acid delivery through stapling and endosomal escape domain.

Cell-penetrating peptides (CPPs) are crucial for delivering macromolecules such as nucleic acids into cells. This study investigates the effectiveness of dual-modified penetratin peptides, focusing on the impact of stapling structures and an endosomal escape domain (EED) on enhancing intracellular uptake. Some CPPs were synthesized with an EED at either the N- or C-terminus and stapling structures, and then complexed with plasmid DNA (pDNA) to evaluate their cellular uptake. Results revealed that the combination of stapling and an EED significantly improved delivery efficiency, primarily via macropinocytosis and clathrin-mediated endocytosis. These findings underscore the importance of optimizing CPP sequences for effective nucleic acid delivery systems.

GSK3B inhibition reduced cervical cancer cell proliferation and migration by modulating the PI3K/Akt signaling pathway and epithelial-to-mesenchymal transition.

Previous studies show that glycogen synthase kinase 3ß (GSK3B) plays an important role in tumorigenesis. However, its role in cervical cancer is unclear. The present study silenced GSK3B with siRNAs and/or chemical inhibitors to determine its role in HeLa cervical cancer cell proliferation and migration as well as in xenograft tumor growth. Cell Counting Kit (CCK)-8 and 5-ethynyl-2'-deoxyuridine (EdU) assays were used to determine cell survival and proliferation. Scratch and Transwell® assays were used to evaluate cell migration. Xenograft tumors were used to evaluate the effect of GSK3B on tumor growth. Transcriptomic sequencing was used to clarify the mechanisms underlying the foregoing processes. Public databases and clinical specimens showed that GSK3B was upregulated in cervical cancer tissues and correlated with poor prognosis. In vitro experiments indicated that GSK3B inhibition reduced cell viability, proliferation, and migration. In vivo experiments demonstrated that GSK3B inhibition slowed xenograft tumor growth. Transcriptomic sequencing revealed that GSK3B inhibition modulated the phosphatidylinositol 3-carboxykinase (PI3K)/protein kinase B (Akt) and extracellular matrix (ECM)-receptor interaction signaling pathways. GSK3B inhibition decreased the protein levels of phosphorylated PI3K and Akt and the levels of mesenchymal markers but increased those of epithelial markers. An activator of the PI3K/Akt signaling pathway counteracted the suppressive effects of GSK3B inhibition on HeLa cell viability and proliferation and on PI3K/Akt signaling. Our data suggested that GSK3B regulated cervical cancer cell proliferation and migration by modulating the PI3K/Akt signaling pathway and epithelial-to-mesenchymal transition (EMT).

Rapid and reversible dissolution of biomolecular condensates using light-controlled recruitment of a solubility tag.

Biomolecular condensates are broadly implicated in both normal cellular regulation and disease. Consequently, several chemical biology and optogenetic approaches have been developed to induce phase separation of a protein of interest. However, few tools are available to perform the converse function - dissolving a condensate of interest on demand. Such a tool would aid in testing whether the condensate plays specific functional roles. Here we show that light-gated recruitment of a solubilizing domain, maltose-binding protein (MBP), results in rapid and controlled dissolution of condensates formed from proteins of interest. Our optogenetic MBP-based dissolution strategy (OptoMBP) is rapid, reversible, and can be spatially controlled with subcellular precision. We also provide a proof-of-principle application of OptoMBP by disrupting condensation of the oncogenic fusion protein FUS-CHOP and reverting FUS-CHOP driven transcriptional changes. We envision that the OptoMBP system could be broadly useful for disrupting constitutive protein condensates to probe their biological functions.

GC-MS analysis, molecular docking, and apoptotic-based cytotoxic effect of Caladium lindenii Madison extracts toward the HeLa cervical cancer cell line.

Utilizing medicinal plants and other natural resources to prevent different types of human cancers is the prime focus of attention. Cervical cancer in women ranks as the fourth most common type of malignancy. The current study used gas chromatography-mass spectrometry (GC-MS) to identify the active phytochemical constituents from Caladium lindenii leaf extracts using ethanol (ECL) and n-hexane (HCL) solvents. Plant extracts were tested for potential cytotoxic effects on HeLa and HEK-293 T cells using the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) and the crystal violet assays. SYBR Green-based real-time PCR was performed to assess the mRNA expression profile of the apoptosis biomarkers (BCL-2 and TP53). The molecular interaction of the compounds with the targeted proteins (TP53, BCL2, EGFR, and HER2) was determined using molecular docking. GC-MS analysis revealed a total of 93 compounds in both extracts. The ECL extract significantly reduced the proliferation of HeLa cervical cancer cells, with an IC50 value of 40 µg/mL, while HEK-293 T cells showed less effect (IC50 = 226 µg/mL). The quantitative RT-PCR gene expression analysis demonstrated the ethanol extract regulated TP53 and BCL2 mRNA expressions in treated cancer cell samples. Heptanediamide, N,N'-di-benzoyloxy-(- 10.1) is the best-docked ligand with a TP53 target found in the molecular docking study, whereas EGFR/Clionasterol had the second highest binding affinity (- 9.7), followed by EGFR/Cycloeucalenol (- 9.6). It is concluded that ECL extract has promising anti-cervical cancer potential and might be valued for developing new plant-derived anticancer agents after further investigations.

Label-free, non-contact determination of resting membrane potential using dielectrophoresis.

Measurement of cellular resting membrane potential (RMP) is important in understanding ion channels and their role in regulation of cell function across a wide range of cell types. However, methods available for the measurement of RMP (including patch clamp, microelectrodes, and potential-sensitive fluorophores) are expensive, slow, open to operator bias, and often result in cell destruction. We present non-contact, label-free membrane potential estimation which uses dielectrophoresis to determine the cytoplasm conductivity slope as a function of medium conductivity. By comparing this to patch clamp data available in the literature, we have demonstratet the accuracy of this approach using seven different cell types, including primary suspension cells (red blood cells, platelets), cultured suspension cells (THP-1), primary adherent cells (chondrocytes, human umbilical mesenchymal stem cells), and adherent (HeLa) and suspension (Jurkat) cancer cell lines. Analysis of the effect of ion channel inhibitors suggests the effects of pharmaceutical agents (TEA on HeLa; DMSO and neuraminidase on red blood cells) can also be measured. Comparison with published values of membrane potential suggest that the differences between our estimates and values recorded by patch clamp are accurate to within published margins of error. The method is low-cost, non-destructive, operator-independent and label-free, and has previously been shown to allow cells to be recovered after measurement.

Synergistic cytotoxicity of olive leaf extract-loaded lipid nanocarriers combined with Newcastle disease virus against cervical cancer cells.

Despite recent medical progress, cervical cancer remains a major global health concern for women. Current standard treatments have limitations such as non-specific toxicity that necessitate development of safer and more effective therapeutic strategies. This research evaluated the combinatorial effects of olive leaf extract (OLE), rich in anti-cancer polyphenols, and the oncolytic Newcastle disease virus (NDV) against human cervical cancer cells. OLE was efficiently encapsulated (>94% loading) within MF59 lipid nanoparticles and nanostructured lipid carriers (NLCs; contains Precirol as NLC-P, contains Lecithin as NLC-L) to enhance stability, bioavailability, and targeted delivery. Physicochemical analysis confirmed successful encapsulation of OLE within nanoparticles smaller than 150 nm. In vitro cytotoxicity assays demonstrated significantly higher toxicity of the OLE-loaded nanoparticle formulations on HeLa cancer cells versus HDF normal cells (P<0.05). MF59 achieved the highest encapsulation efficiency, while NLC-P had the best drug release profile. NDV selectively infected and killed HeLa cells versus HDF cells. Notably, combining NDV with OLE-loaded nanoparticles led to significantly enhanced synergistic cytotoxicity against cancer cells (P<0.05), with NLC-P (OLE) and NDV producing the strongest effects. Apoptosis and cell cycle analyses confirmed the increased anti-cancer activity of the combinatorial treatment, which induced cell cycle arrest. This study provides evidence that co-delivery of OLE-loaded lipid nanoparticles and NDV potentiates anti-cancer activity against cervical cancer cells in vitro through a synergistic mechanism, warranting further development as a promising alternative cervical cancer therapy.

Near-infrared and multifunctional fluorescent probe enabled by cyanopyridine cyanine dye for bisulfite recognition and biological imaging.

SO2 derivatives, sulfite/bisulfite, are widely employed in both the food processing and drug synthesis industries. Despite their widespread application, excessive levels of sulfite/bisulfite can negatively impact human health. Most probes for detecting sulfite/bisulfite are restricted by their fluorescence within the visible spectrum range and poor solubility in aqueous solution, which limit their use in food testing and biological imaging. Herein, a near-infrared probe comprising of the cyanopyridine cyanine skeleton, 4-((Z)-2-((E)-2-chloro-3-(2-cyano-2-(1-methylpyridine-4(1H)-ylidene)ethylidene)cyclohex-1-en-1-yl)-1-cyanovinyl)-1-methylpyridin-1-ium (abbreviated as CCP), was developed. This probe enables precise quantification of bisulfite (HSO3-) in almost pure buffered solutions, showing a near-infrared fluorescence emission at 784 nm with an impressively low detection limit of 0.32 µM. The probe stands out for its exceptional selectivity, minimal susceptibility to interference, and strong adaptability. The probe CCP utilizes the CC bond to trigger a near-infrared fluorescence quenching reaction with HSO3- via nucleophilic addition, which effectively disrupts the large delocalization within the molecule for accurate HSO3- identification. Moreover, the probe has been successfully applied in detecting HSO3- in various food products and living cells, simplifying the measurement of HSO3- content in water samples. This advancement not only enhances the analytical capabilities but also contributes to ensuring food safety and environmental protection. ENVIRONMENTAL IMPLICATION: SO2 derivatives including sulfite/bisulfite, serving dual roles as preservatives and antioxidants, have widespread application across various sectors including food preservation, water sanitation, and the pharmaceutical industry. Despite their widespread application, excessive levels of sulfite/bisulfite can affect human health. Developing methods for precisely and sensitively detecting sulfite/bisulfite in food products and biological samples is important for ensuring food safety and environmental protection. Here, a sensitive near-infrared and multifunctional fluorescent probe in a 99.9 % buffered solution, along with water gel encapsulation, has been successfully applied for the detection of bisulfite in food, authentic water samples, and biological cells.

Contrasting Photosensitized Processes of Ru(II) Polypyridyl Structural Isomers Containing Linear and Hooked Intercalating Ligands Bound to Guanine-Rich DNA.

The DNA binding and cellular uptake of the lambda enantiomer of two bis-tetraazaphenanthrene (TAP) Ru(II) polypyridyl complexes containing either a linear dppn (1) or a hooked bdppz (2) benzodipyridophenazine ligand are reported, and the role of different charge-transfer states of the structural isomers in the photo-oxidation of guanine is explored. Both complexes possess characteristic metal-to-ligand charge-transfer (MLCT) bands between 400 and 500 nm and emission at ca. 630 nm in an aerated aqueous solution. Transient visible absorption (TrA) spectroscopy reveals that 400 nm excitation of 1 yields a dppn-based metal-to-ligand charge-transfer (MLCT) state, which in turn populates a dppn intraligand (3IL) state. In contrast, photoexcitation of 2 results in an MLCT state on the TAP ligand and not the intercalating bdppz ligand. Both 1 and 2 bind strongly to double-stranded guanine-rich DNA with a loss of emission. Combined TrA and time-resolved infrared (TRIR) spectroscopy confirms formation of the guanine radical cation when 2 is bound to the d(G5C5)2 duplex, which is not the case when 1 is bound to the same duplex and indicates a different mechanism of action in DNA. Utilizing the long-lived triplet excited lifetime, we show good uptake and localization of 2 in live cells as well as isolated chromosomes. The observed shortening of the excited-state lifetime of 2 when internalized in cell chromosomes is consistent with DNA binding and luminescent quenching due to guanine photo-oxidation.

Role of charge in enhanced nuclear transport and retention of graphene quantum dots.

The nuclear pore complexes on the nuclear membrane serve as the exclusive gateway for communication between the nucleus and the cytoplasm, regulating the transport of various molecules, including nucleic acids and proteins. The present work investigates the kinetics of the transport of negatively charged graphene quantum dots through nuclear membranes, focusing on quantifying their transport characteristics. Experiments are carried out in permeabilized HeLa cells using time-lapse confocal fluorescence microscopy. Our findings indicate that negatively charged graphene quantum dots exhibit rapid transport to the nuclei, involving two distinct transport pathways in the translocation process. Complementary experiments on the nuclear import and export of graphene quantum dots validate the bi-directionality of transport, as evidenced by comparable transport rates. The study also shows that the negatively charged graphene quantum dots possess favorable retention properties, underscoring their potential as drug carriers.

Real-Time Monitoring of mtDNA Aggregation and Mitophagy Induced by a Fluorescent Platinum Complex in Living Cells.

Mitochondrial DNA (mtDNA) is pivotal for mitochondrial morphology and function. Upon mtDNA damage, mitochondria undergo quality control mechanisms, including fusion, fission, and mitophagy. Real-time monitoring of mtDNA enables a deeper understanding of its effect on mitochondrial function and morphology. Controllable induction and real-time tracking of mtDNA dynamics and behavior are of paramount significance for studying mitochondrial function and morphology, facilitating a deeper understanding of mitochondria-related diseases. In this work, a fluorescent platinum complex was designed and developed that not only induces mitochondrial DNA (mtDNA) aggregation but also triggers mitochondrial autophagy (mitophagy) through the MDV pathway for damaged mtDNA clearance in living cells. Additionally, this complex allows for the real-time monitoring of these processes. This complex may serve as a valuable tool for studying mitochondrial microautophagy and holds promise for broader applications in cellular imaging and disease research.

Mitochondrial-derived compartments are multilamellar domains that encase membrane cargo and cytosol.

Preserving the health of the mitochondrial network is critical to cell viability and longevity. To do so, mitochondria employ several membrane remodeling mechanisms, including the formation of mitochondrial-derived vesicles (MDVs) and compartments (MDCs) to selectively remove portions of the organelle. In contrast to well-characterized MDVs, the distinguishing features of MDC formation and composition remain unclear. Here, we used electron tomography to observe that MDCs form as large, multilamellar domains that generate concentric spherical compartments emerging from mitochondrial tubules at ER-mitochondria contact sites. Time-lapse fluorescence microscopy of MDC biogenesis revealed that mitochondrial membrane extensions repeatedly elongate, coalesce, and invaginate to form these compartments that encase multiple layers of membrane. As such, MDCs strongly sequester portions of the outer mitochondrial membrane, securing membrane cargo into a protected domain, while also enclosing cytosolic material within the MDC lumen. Collectively, our results provide a model for MDC formation and describe key features that distinguish MDCs from other previously identified mitochondrial structures and cargo-sorting domains.

Fast and deep phosphoproteome analysis with the Orbitrap Astral mass spectrometer.

Owing to its roles in cellular signal transduction, protein phosphorylation plays critical roles in myriad cell processes. That said, detecting and quantifying protein phosphorylation has remained a challenge. We describe the use of a novel mass spectrometer (Orbitrap Astral) coupled with data-independent acquisition (DIA) to achieve rapid and deep analysis of human and mouse phosphoproteomes. With this method, we map approximately 30,000 unique human phosphorylation sites within a half-hour of data collection. The technology is benchmarked to other state-of-the-art MS platforms using both synthetic peptide standards and with EGF-stimulated HeLa cells. We apply this approach to generate a phosphoproteome multi-tissue atlas of the mouse. Altogether, we detect 81,120 unique phosphorylation sites within 12 hours of measurement. With this unique dataset, we examine the sequence, structural, and kinase specificity context of protein phosphorylation. Finally, we highlight the discovery potential of this resource with multiple examples of phosphorylation events relevant to mitochondrial and brain biology.

Mechanism and regulation of cargo entry into the Commander endosomal recycling pathway.

Commander is a multiprotein complex that orchestrates endosomal recycling of integral cargo proteins and is essential for normal development. While the structure of this complex has recently been described, how cargo proteins are selected for Commander-mediated recycling remains unclear. Here we identify the mechanism through which the unstructured carboxy-terminal tail of the cargo adaptor sorting nexin-17 (SNX17) directly binds to the Retriever sub-complex of Commander. SNX17 adopts an autoinhibited conformation where its carboxy-terminal tail occupies the cargo binding groove. Competitive cargo binding overcomes this autoinhibition, promoting SNX17 endosomal residency and the release of the tail for Retriever association. Furthermore, our study establishes the central importance of SNX17-Retriever association in the handover of integrin and lipoprotein receptor cargoes into pre-existing endosomal retrieval sub-domains. In describing the principal mechanism of cargo entry into the Commander recycling pathway we provide key insight into the function and regulation of this evolutionary conserved sorting pathway.

Trimethylguanosine cap-fluorescent molecular rotor (TMG-FMR) conjugates are potent, specific snurportin1 ligands enabling visualization in living cells.

The trimethylguanosine (TMG) cap is a motif present inter alia at the 5' end of small nuclear RNAs, which are involved in RNA splicing. The TMG cap plays a crucial role in RNA processing and stability as it protects the RNA molecule from degradation by exonucleases and facilitates its export from the nucleus. Additionally, the TMG cap plays a role in the recognition of snRNA by snurportin, a protein that facilitates nuclear import. TMG cap analogs are used in biochemical experiments as molecular tools to substitute the natural TMG cap. To expand the range of available TMG-based tools, here we conjugated the TMG cap to Fluorescent Molecular Rotors (FMRs) to open the possibility of detecting protein-ligand interactions in vitro and, potentially, in vivo, particularly visualizing interactions with snurportin. Consequently, we report the synthesis of 34 differently modified TMG cap-FMR conjugates and their evaluation as molecular probes for snurportin. As FMRs we selected three GFP-like chromophores (derived from green fluorescent protein) and one julolidine derivative. The evaluation of binding affinities for snurportin showed unexpectedly a strong stabilizing effect for TMGpppG-derived dinucleotides containing the FMR at the 2'-O-position of guanosine. These newly discovered compounds are potent snurportin ligands with nanomolar KD (dissociation constant) values, which are two orders of magnitude lower than that of natural TMGpppG. The effect is diminished by ∼50-fold for the corresponding 3'-regioisomers. To deepen the understanding of the structure-activity relationship, we synthesized and tested FMR conjugates lacking the TMG cap moiety. These studies, supported by molecular docking, suggested that the enhanced affinity arises from additional hydrophobic contacts provided by the FMR moiety. The strongest snurportin ligand, which also gave the greatest fluorescence enhancement (Fm/F0) when saturated with the protein, were tested in living cells to detect interactions and visualize complexes by fluorescence lifetime monitoring. This approach has potential applications in the study of RNA processing and RNA-protein interactions.

Gel-Assisted Proteome Position Integral Shift Assay Returns Molecular Weight to Shotgun Proteomics and Identifies Caspase 3 Substrates.

Here, we present a high-throughput virtual top-down proteomics approach that restores the molecular weight (MW) information in shotgun proteomics and demonstrates its utility in studying proteolytic events in programmed cell death. With gel-assisted proteome position integral shift (GAPPIS), we quantified over 7000 proteins in staurosporine-induced apoptotic HeLa cells and identified 84 proteins exhibiting in a statistically significant manner at least two of the following features: (i) a negative MW shift; (ii) an elevated ratio in a pair of a semitryptic and tryptic peptide, (iii) a negative shift in the standard deviation of MW estimated for different peptides, and (iv) a negative shift in skewness of the same data. Of these proteins, 58 molecules were previously unreported caspase 3 substrates. Further analysis identified the preferred cleavage sites consistent with the known caspase cleavages after the DXXD motif. As a powerful tool for high-throughput MW analysis simultaneously with the conventional expression analysis, the GAPPIS assay can prove useful in studying a broad range of biological processes involving proteolytic events.

CLASP-mediated competitive binding in protein condensates directs microtubule growth.

Microtubule organization in cells relies on targeting mechanisms. Cytoplasmic linker proteins (CLIPs) and CLIP-associated proteins (CLASPs) are key regulators of microtubule organization, yet the underlying mechanisms remain elusive. Here, we reveal that the C-terminal domain of CLASP2 interacts with a common motif found in several CLASP-binding proteins. This interaction drives the dynamic localization of CLASP2 to distinct cellular compartments, where CLASP2 accumulates in protein condensates at the cell cortex or the microtubule plus end. These condensates physically contact each other via CLASP2-mediated competitive binding, determining cortical microtubule targeting. The phosphorylation of CLASP2 modulates the dynamics of the condensate-condensate interaction and spatiotemporally navigates microtubule growth. Moreover, we identify additional CLASP-interacting proteins that are involved in condensate contacts in a CLASP2-dependent manner, uncovering a general mechanism governing microtubule targeting. Our findings not only unveil a tunable multiphase system regulating microtubule organization, but also offer general mechanistic insights into intricate protein-protein interactions at the mesoscale level.